JP5875035B2 - Electrode member and manufacturing method thereof - Google Patents

Description

  The present invention relates to an electrode member, particularly a titanium electrode member and a method for manufacturing the same. This electrode member has various organic molecules or inorganic substances, organic / inorganic composites, metal complexes, biomolecules including enzymes, or one or more types of catalysts such as molecular catalysts (hereinafter referred to as catalysts) on the surface thereof. By fixing, it can be suitably used for electrodes of water electrolysis devices, fuel cells, solar cells, sensors and the like.

  Titanium oxide is used as an electrode for a dye-sensitized solar cell or an electrode for water decomposition because it can fix a catalyst on its surface. And, as the electrode fixing area increases, the amount of the modified catalyst increases and the water resolution and battery output increase, so it is desirable to increase the surface area (= specific surface area) per unit volume of the electrode. It is rare. Further, in order for the catalyst to be stably fixed for a long period of time, it is necessary for the surface to have a function that allows the electrode surface to be chemically bonded thereto. Furthermore, in order for electrons generated in the catalyst to be effectively propagated, it is essential to improve the conductivity of titanium oxide that generally exhibits little conductivity. Therefore, various methods for manufacturing a titanium electrode having these properties have been proposed.

  First, in order to make an electrode having a large specific surface area, a method of blasting or etching the electrode surface is known.

  In order to improve the conductivity of titanium oxide, the surface of the substrate is coated with a solution containing a complex of titanium alkoxide and a chelating agent, which is fired in a reducing atmosphere (H 2, CO, etc.) and heated ( Patent Document 1), Titanium alkoxide solution is reacted with a fluorine-containing solution (Patent Document 2), a doping solution containing lithium is applied to a predetermined portion, and then heat treated (Patent Document 3). Titanium alkoxide and niobium or tantalum alkoxide Mixing the solution and applying it on a transparent substrate (Patent Document 4), hot pressing titanium oxide in a non-oxidizing atmosphere such as argon or nitrogen (Patent Document 5), and introducing oxygen defects It is known to do.

  It is also known to improve the conductivity of titanium oxide by introducing hydrogen by RF plasma treatment of a titanium oxide film formed by sputtering in a hydrogen atmosphere (Patent Document 6). Furthermore, a metal nitride is applied on the substrate and the surface of the nitride is oxidized to form a metal oxide layer (Patent Document 7), and titanium oxide nanoparticles are applied to the surface of a conductive glass substrate such as ITO. Sintering and fixing (Non-Patent Document 1) has also been proposed.

JP-A-10-146530 JP-A-9-118524 JP-A-9-265832 JP 2010-225468 JP 2008-57045 A JP-A-10-226598 JP 2006-210341 A

B. O'Regan, M.M. Gratzel, Nature, 353, 737, 1991.

However, the conventional technique for producing an electrode having a large specific surface area cannot improve the conductivity of titanium oxide. On the other hand, all of the conventional techniques for improving the conductivity of titanium oxide are based on the premise that the starting material is a flat plate, and thus the obtained electrode has a low specific surface area. In addition, with the technique described in Non-Patent Document 1, it is difficult to firmly bond the titanium oxide particles to the substrate. Therefore, in the conventional technique, if one problem is to be realized, the other problem must be sacrificed.
Therefore, an object of the present invention is to provide an electrode member that can utilize the properties of titanium oxide capable of chemically fixing a catalyst for a long period of time, has a large specific surface area, and is excellent in conductivity. .

In order to solve the problem, the electrode member of the present invention is
A substrate made of titanium or a titanium alloy;
Surface of 0.1 to 10 μm thickness formed on the surface of the base material, comprising at least a titanium oxide phase and optionally a titanium nitride phase, and having a comb-like structure including a large number of columnar crystals having a thickness of 1 to 100 nm And a layer.

According to the electrode member of the present invention, since the surface layer includes at least a titanium oxide phase, the catalyst can be chemically and stably fixed for a long period of time. Since the surface layer has a comb structure including the columnar crystals , it has a large specific surface area, a large amount of catalyst modification per unit volume, and excellent reaction efficiency. Here, the comb shape refers to a shape in which columnar crystals extend away from the substrate like comb teeth as shown in FIG. 1 when the surface of the substrate is the back of a comb. Titanium constituting the columnar crystal titanium oxide is derived from titanium or titanium alloy in the base material, and the surface layer is formed continuously from the base material, so the surface layer is strongly fixed to the base material. Has been. Moreover the titanium oxide may be one having an oxygen defect as represented by TiO _2-x, thereby having electrical conductivity. Also, part of the surface layer in order to improve the conductivity is constituted by a phase of titanium nitride.

When sufficient oxygen defects and / or a considerable amount of titanium nitride phase are included, the specific resistance of the surface layer is 1.0 × 10 ⁶ Ωcm or less, and electrons generated in the catalyst are efficiently propagated. If the thickness of the surface layer is smaller than 0.1 μm, the amount of catalyst modification becomes too small to make it difficult to exert the catalytic function, and if it exceeds 10 μm, the conductivity is lowered and the possibility of peeling from the substrate There is.

A suitable method for manufacturing the electrode member of this invention is:
Alkali-acid treatment step of forming a surface layer with a hydrated comb structure on the surface of the substrate by immersing the substrate made of titanium or titanium alloy in an alkaline aqueous solution and then immersing in water or an acidic aqueous solution When,
A dehydration step of dehydrating the surface layer by heating the base material that has undergone the alkali-acid treatment;
And a conductive step of treating the surface layer in a nitrogen gas atmosphere.

By immersing a base material made of titanium or a titanium alloy in an alkaline aqueous solution, the surface of the base material has a comb structure including a large number of columnar crystals made of sodium hydrogen titanate and having a thickness of 1 to 100 nm. A layer of 10 μm is formed. Accordingly, the specific surface area of the substrate surface is remarkably increased at this stage. Subsequently, the base material is immersed in water or an acidic aqueous solution, and washed with water as necessary to remove the alkali component and maintain the previously formed structure (such as H ₂ Ti ₃ O ₇ ). A layer is formed.

In order to further increase the specific surface area, the base material may be a porous body having communication holes having a pore diameter of 50 μm to 3 mm. It is possible to further increase the specific surface area by forming the surface layer having a comb structure on the inner surface of the hole of the porous body.
As a porous body, a structure in which holes are connected by a passage, a structure in which through holes are arranged in a straight line and they are bundled, a structure in which folded plates are stacked in a small gap, and a large number of rectangular parallelepipeds having columnar holes are bundled Various porous structures such as a honeycomb structure (honeycomb shape) can be mentioned.
The method of making the porous body is to sinter powder, make a structure that can be intentionally designed with laser foam, form a groove with a plate with holes, and fold the plate to make a small gap For example, they can be stacked, folded into a number of U-shapes, and stacked. Of these, the method of bending the plate is considered to be the least costly manufacturing method.

Thereafter, when heat treatment is performed, titanic acid is dehydrated to form titanium oxide crystals. When the heat treatment is performed in the air, the surface layer obtained at this stage contains a small amount of oxygen defects but is poor in conductivity. Therefore, the surface layer is treated under a nitrogen gas atmosphere. Examples of the treatment means under a nitrogen gas atmosphere include heating in a nitrogen gas atmosphere substantially free of oxygen, or plasma treatment in the same atmosphere. As a result, oxygen diffuses and many oxygen defects are formed and / or titanium nitride is formed, thereby increasing conductivity. As the crystal phase, the higher the treatment temperature in the nitrogen gas atmosphere, the greater the amount of Ti ₄ O ₇ or Ti ₂ O _{3 and} the amount of titanium nitride than TiO ₂ . Further, heating in a nitrogen gas atmosphere and plasma treatment may be combined. In either case, the comb structure is not impaired.

  In general, the Ti—O bond of titanium oxide is so strong that it is difficult to replace oxygen with nitrogen. Therefore, heating in a nitrogen gas atmosphere causes oxygen defects in the outermost layer portion and causes a reaction between titanium metal on the substrate surface (near the boundary between the substrate and the surface layer) and nitrogen with priority, Nitrogen can be efficiently introduced into the deep part of the surface layer. On the other hand, the plasma treatment can efficiently introduce nitrogen into the outermost layer. Therefore, by combining the two, the conductivity can be increased more than any one of them.

Since the heating temperature in the nitrogen gas atmosphere may be as high as about 1000 ° C., the dehydration process is performed by simultaneously performing dehydration and nitridation by performing the heating for dehydration in the nitrogen gas atmosphere. You may make it serve as a process. On the other hand, when nitriding is performed by plasma processing alone, it is preferable to perform both processes separately because the plasma processing cannot be performed at such a high temperature.
In this way, the surface layer is modified so as to contain at least titanium oxide capable of chemically fixing the catalyst and to cause oxygen deficiency in a part thereof and / or to become a phase of titanium nitride.

  As described above, the electrode member of the present invention has a large specific surface area, exhibits electrical conductivity, and the surface layer capable of chemically fixing the catalyst is strongly bonded to the base material. When used in electrodes for cracking devices, fuel cells, solar cells, sensors, etc., it contributes to improving reaction efficiency and durability.

FE showing each surface (upper) and cross-section (lower) of an inner (left), outer (center), and reference titanium flat plate (right) of a porous titanium metal heat-treated in a nitrogen atmosphere after alkali-acid treatment -SEM photograph. It is a general-view figure of the titanium metal porous body which is one of the base materials. It is a graph which shows the thin film X-ray diffraction pattern of the titanium metal plate surface which performed each process. It is a graph which shows the glow discharge emission-spectral-analysis (GD-OES: Glow Discharge-Optical Emission Spectroscopy) result vicinity of the titanium metal plate surface heat-processed in nitrogen atmosphere after alkali-acid treatment. It is a graph which shows the scratch strength of the titanium metal plate surface which performed each process. It is a graph which shows the result of the X-ray photoelectron spectroscopy (XPS: X-ray photoelectron spectroscopy) vicinity of the titanium metal plate surface heat-processed in nitrogen atmosphere after alkali-acid treatment.

  The surface layer preferably has a nitrogen concentration of 1 atomic% or more in a depth range of 1 μm from the surface. This is because if it is less than 1 atomic%, it does not exhibit much conductivity. On the other hand, if the nitrogen concentration is too high, titanium oxide necessary for catalyst modification is relatively reduced, which is not preferable. However, nitrogen introduction is not so easy, and no treatment conditions that can introduce 15 atomic% or more have been found in the current technical level.

  A preferable alkali concentration of the alkaline aqueous solution is 0.1 to 10M, and an aqueous solution in which one or more alkalis selected from sodium hydroxide and potassium hydroxide are dissolved is preferably used. In any case, preferable immersion temperatures are 5 to 99 ° C. and 0.5 to 48 hours. If any one of the conditions is less than the lower limit, a surface layer having the preferred thickness, specific surface area, or gradient composition is difficult to form, and if the upper limit is exceeded, the surface layer formed thereafter becomes too thick and becomes conductive. As well as lowering the properties, it becomes easy to peel off from the substrate.

  A preferable acid concentration of the acidic aqueous solution is 0.5 M or less, and an aqueous solution in which one or more acids selected from hydrochloric acid, nitric acid, and sulfuric acid are dissolved is preferably used. In any case, preferable immersion temperatures are 5 to 99 ° C. and 0.5 to 48 hours. If any one of the conditions is less than the lower limit, the alkali component cannot be sufficiently removed, and the titanic acid layer is difficult to be formed. If the upper limit is exceeded, the comb structure is dissolved and the specific surface area is greatly reduced. The possibility increases.

  The heating temperature for dehydrating the surface layer is preferably 400 to 1000 ° C. When the temperature is lower than 400 ° C., crystalline titanium oxide is hardly formed, and the mechanical strength and chemical stability of the titanium oxide are low. When the temperature exceeds 1000 ° C., the comb structure is densified, the specific surface area is greatly reduced, the surface layer becomes too thick, and is easily peeled off due to a difference in thermal expansion.

  When the nitridation is performed by plasma treatment, a preferable output is 10 to 1000 W.

[Production conditions]
Example 1
A fine pure titanium metal plate having a size of 10 × 10 × 1 mm was polished with a # 400 diamond pad, and ultrasonically washed with acetone, 2-propanol, and ultrapure water in order for 30 minutes each, and then 5M It was immersed in 5 ml of an aqueous sodium hydroxide solution at 60 ° C. for 1 hour (hereinafter referred to as “alkali treatment”) and washed with ultrapure water for 30 seconds. This titanium metal plate was immersed in 10 ml of 0.5 mM hydrochloric acid at 40 ° C. for 3 hours (hereinafter referred to as “acid treatment”) and washed with ultrapure water for 30 seconds. Next, the titanium metal plate is heated from room temperature to 600 ° C. in an electric furnace under a nitrogen atmosphere, held at 600 ° C. for 1 hour, and then slowly cooled (hereinafter referred to as “nitrogen heat treatment”). Samples were prepared.

-Example 2-
In Example 1, a sample was produced under the same conditions as in Example 1 except that the temperature in the nitrogen heat treatment was 700 ° C.

Example 3
In Example 1, a sample was manufactured under the same conditions as in Example 1 except that the temperature in the nitrogen heat treatment was 800 ° C.

Example 4
In Example 1, a sample was manufactured under the same conditions as in Example 1 except that the temperature in the nitrogen heat treatment was set to 900 ° C.

-Example 5
In Example 1, a sample was produced under the same conditions as in Example 1 except that the temperature in the nitrogen heat treatment was 1000 ° C.

-Example 6
A fine pure titanium metal plate having a size of 10 × 10 × 1 mm was polished with a # 400 diamond pad, and ultrasonically washed with acetone, 2-propanol, and ultrapure water in that order for 30 minutes each. 1 was subjected to alkali treatment under the same conditions. This titanium metal plate was acid-treated under the same conditions as in Example 1, and then washed with ultrapure water for 30 seconds. Next, the titanium metal plate was heated from normal temperature to 600 ° C. at a rate of 5 ° C./min in an electric furnace under atmospheric air, held at 600 ° C. for 1 hour, and allowed to cool in the furnace (hereinafter “ Samples were prepared by “atmospheric heat treatment”. Thereafter, a sample was prepared by performing plasma treatment in a nitrogen atmosphere at room temperature (about 20 ° C.) at an output of 100 W for 1 hour (hereinafter referred to as “plasma treatment”).

-Example 7-
In Example 6, a sample was manufactured under the same conditions as in Example 6 except that the temperature in the plasma treatment was 400 ° C.

-Example 8-
A fine pure titanium metal plate having a size of 10 × 10 × 1 mm was polished with a # 400 diamond pad, and ultrasonically washed with acetone, 2-propanol, and ultrapure water in that order for 30 minutes each. 1 was subjected to alkali treatment under the same conditions. This titanium metal plate was acid-treated under the same conditions as in Example 1, and then washed with ultrapure water for 30 seconds. Next, this titanium metal plate was subjected to nitrogen heat treatment under the same conditions as in Example 2. Thereafter, the sample was prepared by plasma treatment under the same conditions as in Example 6.

-Comparative Example 1-
A comparative sample was prepared under the same conditions as in Example 1 except that the nitrogen heat treatment was not performed.
-Comparative Example 2-
The comparative sample obtained in Comparative Example 1 was subjected to atmospheric heat treatment under the same conditions as in Example 6.
-Comparative Example 3-
The comparative sample obtained in Comparative Example 1 was heat-treated under the same conditions as in Example 1 except that the atmosphere in the heat treatment was Ar.

[Conductivity measurement]
When the conductivity of each sample of the example and the comparative example was measured, as shown in Table 1, the conductivity was superior to that of the comparative example 2 in all the examples. In particular, in the samples of Examples 1, 2, 3, 4, 5, and 8, the conductivity was significantly improved.

[Specific surface area measurement]
A dense pure titanium metal plate having a size of 6 × 25 × 1 mm was prepared. The surface area of this titanium metal plate is 3.62 × 10 ⁻⁴ m ² = 362 mm ² (= 6 × 25 × 2 + 6 × 1 × 2 + 25 × 1 × 2), and the density is about 4.5 g / cm ³ . Therefore, the weight is 0.675 g (= 0.6 × 2.5 × 0.1 × 4.5). Therefore, the surface area per unit weight is calculated as 536 mm ^{2 /} g (≈362 ÷ 0.675).

The titanium metal plate to an alkali treatment - acid treatment - After nitrogen heat treatment, using an automatic specific surface area measuring apparatus BELSORP-mini BEL Japan Co., Ltd., was measured specific surface area, 1g per 5.745 × 10 ^{- 2} m ² / g. As a result, it was found that the surface area was about 107 (≈5.745 × 10 ⁻² ÷ 5.36 × 10 ⁻⁴ ) times.

[Surface treatment to porous structure]
When a titanium porous body having a communicating hole having a size of about 10 × 10 × 10 mm, a porosity of 70.1%, and a pore diameter of 0.5 to 3 mm shown in FIG. 2 is treated with an alkali and acid, the porous body is shown in FIG. It was found that the same thickness and nano-sized network structure was uniformly formed inside (a portion having a depth of about 5 mm from the surface) and outside. From these results, it was found that this chemical treatment method can be applied not only to a flat plate sample but also to a porous body.

[Identification of crystal phase]
A titanium metal plate treated under the same conditions as in Examples 1-5 and 8 and Comparative Example 1 was applied to a thin-film X-ray diffractometer, and the crystal phase of the surface layer was analyzed. As shown in FIG. The higher the temperature in the treatment, the more prominent the titanium nitride peak. Further, as the heat treatment temperature becomes higher, the O / Ti ratio (theoretical value = 2) is smaller than that of TiO ₂ , Ti ₄ O ₇ (O / Ti = 1.75), Ti ₂ O ₃ (O / Ti = 1). .) Was confirmed. This is considered to indicate the formation of oxygen defects.

[Measurement of element concentration]
A titanium metal plate treated under the same conditions as in Example 2 and Comparative Example 1 was subjected to a glow discharge spectroscopic analyzer to measure the elemental concentration of the surface layer. As shown in FIG. 4, Comparative Example 1 (left: alkali In the treatment and acid treatment only), hydrogen and oxygen are mostly distributed at a depth of less than 0.1 μm, and in Example 2 (right: nitrogen heat treatment after alkali treatment and acid treatment), oxygen is distributed at a depth of less than 0.1 μm. On the other hand, it was found that a large amount of nitrogen was distributed at a depth deeper than 0.1 μm.

[Scratch strength measurement]
Using a scratch tester CSR-2000 manufactured by Reska Co., Ltd., measure the scratch strength of a sample obtained by subjecting a dense pure titanium metal plate to alkali treatment-acid treatment and heat treatment at 600 ° C. in air, Ar or N _2. did. The measurement was performed by applying an amplitude of 100 μm on the sample to a stylus having a spring constant of 200 g / mm and moving the stylus at a speed of 10 mm / sec while applying a load of 100 mN / min. As a result, as shown in FIG. 5, it was found that the scratch strength was significantly improved by heat treatment in an N ₂ atmosphere.

[Evaluation of nitrogen introduction means]
A titanium metal plate treated under the same conditions as in Examples 1-3, 6, and 7 was applied to an X-ray photoelectron spectrometer and analyzed for the electronic state of nitrogen on the sample surface. As shown in FIG. It was found that the surface nitrogen concentration significantly increased.

[Catalyst fixation evaluation]
A sample treated with alkali-dilute hydrochloric acid-heat treatment under the same conditions as in Example 2 except that the size was 35 × 10 × 1 mm was added to an ethanol solution of ferrocenyl diphosphate (Fc (PO ₃ H ₂ ) ₂ ) in an argon gas atmosphere. The surface layer was modified with ferrocenyl diphosphate by soaking at 100 ° C. for 2 days. This was measured reflection FT-IR for the sample, 1196cm ^-1 (P = O bond) and peaks at 1080cm ^-1 (P-O-Ti bond) was observed. That is, it was recognized that the catalyst was chemically fixed to titanium oxide.

[CV measurement]
The sample treated under the same conditions as in Example 1 was immersed in an ethanol solution of ferrocenyl diphosphoric acid at 100 ° C. for 2 days in an argon gas atmosphere to modify the ferrocenyl diphosphoric acid on the surface layer.
Potentials of 20 mV / s, 40 mV / s, 60 mV / s, 80 mV / s and 100 mV / s from 0 V to 1.0 V (reference electrode: silver / silver chloride, solvent: borate buffer, pH = 7) for this sample Cyclic voltammograms were measured at the sweep rate, and all showed reversible waves based on ferrocene redox with good reproducibility. Further, when the relationship between the sweep rate and the oxidation wave peak current value is plotted, a linear relationship is obtained. From this, the modification amount per unit area of ferrocenyl diphosphate involved in redox on the electrode surface is 5.6 nmol. / Cm ² was calculated.

Claims (12)

A substrate made of titanium or a titanium alloy;
And a surface layer having a thickness of 0.1 to 10 μm which is formed on the surface of the substrate and has a comb-like structure including at least a titanium oxide phase and a titanium nitride phase and including columnar crystals having a thickness of 1 to 100 nm. An electrode member. The electrode member according to claim 1, wherein the specific resistance of the surface layer is 1.0 × 10 ⁶ Ωcm or less. The electrode member according to claim 1, wherein the surface layer has a specific surface area of 1 to 10,000 cm ² / g.   The electrode member according to claim 1, wherein the surface layer contains 1 atomic% or more of nitrogen.   The electrode member according to claim 1, wherein the base material is a porous body having communication holes having a pore diameter of 50 μm to 3 mm, and the surface layer is formed on an inner surface of the communication holes. The electrode member according to any one of claims 1 to 5,
An electrode comprising: a catalyst fixed to a surface layer of the electrode member. Alkali-acid treatment step of forming a surface layer with a hydrated comb structure on the surface of the substrate by immersing the substrate made of titanium or titanium alloy in an alkaline aqueous solution and then immersing in water or an acidic aqueous solution When,
A dehydration step of dehydrating the surface layer by heating the base material that has undergone the alkali-acid treatment;
A method for producing an electrode member, comprising: a step of heating the surface layer in a nitrogen gas atmosphere not containing oxygen and / or plasma treatment in the same atmosphere. The alkali concentration of the alkaline aqueous solution is 0.1 to 10 M, The method of claim 7 acid concentration of said acidic aqueous solution is less than 0.5M.   The method according to claim 7, wherein the heating temperature in the dehydration step is 400 ° C. or higher and 1000 ° C. or lower.   The method according to claim 7, wherein the dehydration step also serves as the conductive step by performing heating in the dehydration step in an atmosphere of nitrogen gas.   The method according to claim 7, wherein the treatment in the conductive step is a plasma treatment.   The method according to claim 11, wherein an output in the plasma treatment is 10 to 1000 W.

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