JP2018123391A - Electrode for generating hydrogen and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode with excellent durability for generating hydrogen that can generate hydrogen by alkaline water electrolysis with a lower hydrogen generation overvoltage than that of conventional cathodes.SOLUTION: An electrode for generating hydrogen of the present invention comprises a conductive substrate and a catalytic layer formed on the conductive substrate, in which platinum is included in the catalytic layer. The diameter of crystallite is 200Å or less according to an x-ray diffraction on the (111) surface of the platinum, and the crystalline phase proportion is 1-15% on the (220) and (311) surfaces of the platinum.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrode for hydrogen generation used for alkaline water electrolysis and a method for producing the same.

  Hydrogen is attracting interest as an energy source that is suitable for storage and transport and has a low environmental impact. Currently, hydrogen is mainly produced by steam reforming of fossil fuels, but from the viewpoint of global warming and fossil fuel depletion, the importance of water electrolysis using renewable energy as a power source has increased. Yes.

  Water electrolysis is roughly divided into three types: alkaline water electrolysis, solid polymer type water electrolysis, and water vapor electrolysis. A proton conductive fluororesin ion exchange membrane is used as an electrolyte for solid polymer water electrolysis, and a platinum-based material such as platinum, a platinum-based alloy, or platinum-supported carbon is used for an electrode. Solid polymer electrolysis is more efficient than alkaline water electrolysis, but is difficult to increase in size because of high member costs.

  Steam electrolysis is a technique for producing hydrogen by electrolyzing steam at about 700 to 800 ° C., and a solid oxide made of ceramic is used as an electrolyte. Because of the high temperature, high efficiency can be expected compared to other water electrolysis systems operating at low temperatures, but the environment in which it can be used is limited. In addition, it is a technology under research and development, and many problems remain in practical use.

  On the other hand, a high-concentration alkaline aqueous solution is used as an electrolyte for alkaline water electrolysis. Alkaline water electrolysis is expected as a method of stably obtaining hydrogen at low cost by electrolyzing alkaline water without using an expensive noble metal catalyst. Alkaline water electrolysis is suitable for large-scale hydrogen production, and can utilize the technology of a large-sized salt electrolyzer. Alkaline water electrolysis is considered to have a high efficiency, and improvement of electrodes is cited as a countermeasure.

The electrode reactions at both electrodes of alkaline water electrolysis are as follows.
Anode reaction: 2OH ⁻ → H ₂ O + 1 / 2O ₂ + 2e ⁻ (1)
Cathode reaction: 2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻ (2)
The cathode used in the alkaline water electrolysis uses a platinum-based fired electrode used in soda electrolysis, or a nickel-based material such as a nickel-plated iron electrode or nickel-based metal electrode (patent) Document 1 and Non-Patent Documents 1 and 2).

JP 2008-240001 A

2013 Patent Application Trend Survey Report (Summary) Electrolytic hydrogen production and related technologies, JPO, p. 24 Hydrogen Energy System, Vol. 36, no. 1 (2001)

  However, the conventional cathode has a problem that the hydrogen generation overvoltage is high and the electrode life is short. It is considered that the firing electrode has a high hydrogen generation overvoltage because the oxidation state is reduced at a negative potential. In addition, the conventional cathode has a problem that platinum is eluted in an alkaline aqueous solution when electrolysis is repeated, resulting in poor durability.

  Accordingly, an object of the present invention is to provide an electrode for hydrogen generation that can generate hydrogen by alkaline water electrolysis with a hydrogen generation overvoltage lower than that of a conventional cathode, and that is excellent in durability, and a method for producing the same.

  As a result of intensive studies, the inventors of the present invention have developed that a hydrogen generating electrode in which the crystallite diameter of platinum contained in the catalyst layer is within a specific range generates hydrogen at a hydrogen generation overvoltage lower than that of a conventional cathode. And it was found to be excellent in durability. Further, it has been found that such an electrode for hydrogen generation can be obtained by plating a conductive base material by electroplating, and setting the alkaline component concentration of the plating bath and the plating bath temperature in a specific range. .

That is, the present invention is as follows.
1. An electrode for hydrogen generation having a conductive substrate and a catalyst layer formed on the conductive substrate, the platinum containing platinum in the catalyst layer, the X-ray on the (111) plane of the platinum An electrode for hydrogen generation having a crystallite diameter by diffraction of 200 mm or less and a crystal phase existence ratio of (220) plane and (311) plane of platinum of 1 to 15%.
2. 2. The electrode for hydrogen generation as described in 1 above, wherein the crystal phase existing ratio of (111) plane by X-ray diffraction of platinum is 40% or more.
3. 3. The hydrogen generation electrode according to 1 or 2, wherein the platinum has an ECSA (electrochemical activity specific surface area) of 5 m ² / g or more.
4). 4. The electrode for hydrogen generation according to any one of 1 to 3, wherein the content of the alkali component in the catalyst layer is 50 ppm or more.
5. The electrode for hydrogen generation according to any one of 1 to 4, wherein the alkaline component is potassium.
6). 6. The electrode for hydrogen generation according to any one of 1 to 5, which is used for alkaline water electrolysis.
7). A method for producing an electrode for hydrogen generation comprising a conductive substrate and a catalyst layer formed on the conductive substrate, wherein the catalyst layer contains platinum.
Plating the conductive substrate by an electroplating method using a plating bath containing platinum, and a plating treatment step of depositing the platinum on the conductive substrate from the plating bath,
The said manufacturing method characterized by the said plating bath containing 40-70 g / L of an alkaline component, and the temperature of this plating bath at the time of this plating process exists in the range of 20 to 60 degreeC.
8). 8. The method for producing an electrode for hydrogen generation as described in 7 above, wherein the alkali component is potassium.

  Compared with the conventional hydrogen generating electrode, the hydrogen generating electrode of the present invention has a crystallite diameter by X-ray diffraction on the (111) plane of platinum contained in the catalyst layer of 200 mm or less, and the platinum ( 220) and (311) planes have a crystal phase existence ratio of 1 to 15%, so that hydrogen generation overvoltage in alkaline water electrolysis is low, and elution of platinum into an alkaline aqueous solution is suppressed, resulting in high durability. Therefore, by using the electrode for hydrogen generation of the present invention for alkaline water electrolysis, the electrode activity can be greatly improved, the amount of catalyst can be reduced even at a large current density, and the durability is excellent. Can be reduced.

FIG. 1 is a diagram showing the results of SEM images, crystallite diameters, crystal phase existence ratios, ECSA, and electrode potentials of the hydrogen generation electrodes prepared in Examples 1 and 2 and Comparative Examples 1 and 2. FIG. 2 is a diagram showing the results of analysis by the X-ray diffraction method of the electrode produced in Example 1. FIG. 3 is a diagram showing the results of analysis by X-ray diffraction of the electrodes produced in Example 1, Example 2, and Comparative Example 1. FIG. 4 is a diagram showing the electrochemical measurement results of the electrodes produced in Example 1, Example 2, and Comparative Example 1. FIG. 5 is a graph showing SEM images, crystallite diameters, crystal phase existence ratios, ECSA, and electrode potentials of the hydrogen generation electrode prepared in Comparative Example 3. FIG. 6 is a diagram showing the electrochemical measurement results of the electrodes produced in Example 1, Example 2, and Comparative Example 3. FIG. 7 is a diagram showing the results of analysis by X-ray diffraction of the electrodes produced in Example 1 and Comparative Example 3.

  Hereinafter, the present invention will be described in detail. The present invention relates to an electrode for hydrogen generation which has a conductive base material and a catalyst layer formed on the conductive base material, and contains platinum in the catalyst layer. Provided is a hydrogen generating electrode in which the crystallite diameter by X-ray diffraction on the plane is 200 mm or less and the crystal phase existing ratio of the (220) plane and the (311) plane is 1 to 15%.

  The catalyst layer possessed by the electrode for hydrogen generation of the present invention means a layer formed on a conductive substrate and having a function of reducing hydrogen generation overvoltage. The catalyst layer contains platinum.

The content of platinum in the catalyst layer, from the viewpoint of cost and durability, is preferably 1 to 50 g / ^{m 2,} more preferably from 5 to 20 g / ^{m 2,} more preferably 5 to 15 g / m ² .

  The crystallite diameter by X-ray diffraction on the (111) plane of platinum contained in the catalyst layer is 200 mm or less, preferably 150 mm or less, more preferably 120 mm or less. Further, the crystal phase existing ratio of the (220) plane and (311) plane of platinum is 1 to 15%, preferably 5 to 15%, more preferably 10 to 15%. By satisfying these conditions, the reaction specific surface area increases, so that the hydrogen generation overvoltage can be kept low, and the durability is also excellent because of high crystallinity. The crystal phase existing ratio of the (111) plane of platinum is preferably 40% or more, more preferably 45% or more, and most preferably 50% or more. Further, the proportion of the crystal phase present in the (222) plane of platinum contained in the catalyst layer is preferably 1 to 5%, more preferably 1 to 4%, and further preferably 2 to 3%. preferable. If the crystal phase existing ratio of the (222) plane of platinum is 1 to 5%, the hydrogen generation overvoltage can be further reduced, and the durability is improved.

The crystallite diameter in the (111) plane of platinum and the proportion of each crystal phase present indicating the orientation of the platinum crystal can be determined by X-ray diffraction, and the crystallite diameter in (111) plane is determined by the following equation. Can do. The crystal phase existence ratio is calculated from the integrated intensity ratio of each peak.
Crystallite diameter: D = (Κ · λ) / (β · cos θ)
Κ: Sherler constant (= 0.94)
λ: Wavelength of the X-ray tube used β: Spread of diffraction line depending on crystallite size θ: Diffraction angle

  The proportion of the crystal phase present on the (111) plane of platinum by X-ray diffraction is preferably 40% or more, more preferably 45% or more. When the proportion of the crystal phase on the (111) plane is 40% or more, the hydrogen adsorption energy becomes appropriate, so that the hydrogen generation overvoltage can be kept low. Although an upper limit is not specifically limited, Usually, it is preferable that it is 80% or less, and it is more preferable that it is 70% or less. If the crystal phase existing ratio of the (111) plane exceeds 80%, durability may be reduced and Pt may be eluted. The crystal phase existence ratio of the (111) plane is obtained by calculating the integrated intensity of each platinum crystal plane.

The crystallite diameter of platinum by X-ray diffraction and the crystal phase existence ratio of (220) plane, (311) plane, (111) plane, and (222) plane of platinum are the temperature, current density, and plating in the electroplating method described later. It can adjust by adjusting conditions, such as pH of a bath and content of the alkali component in a plating bath. Specific conditions will be described in detail in the description of the production method below. For example, the temperature of the electroplating method is preferably 20 to 60 ° C., the current density is preferably 1 to 3 A / dm ² , more preferably 2. The conditions which make content of an alkaline component 40-70 g / L are -3A / dm < ² >.

The ECSA (Electrochemical Surface Area) of platinum contained in the catalyst layer is preferably 5 m ² / g or more, more preferably 10 m ² / g or more, and further preferably 15 m ² / g or more. It is. When the ECSA in the catalyst layer is 5 m ² / g or more, since there are many active sites, the hydrogen generation overvoltage can be kept low.

ECSA is calculated from the amount of electricity of the hydrogen atom adsorption wave by the following equation.
ECSA [cm ² / g] = QH [μC] / (210 [μC / cm ² ] × platinum mass [g])
QH: hydrogen adsorption charge amount 210 μC / cm ² : adsorption charge amount per unit active area of platinum

The ECSA of the platinum can be adjusted by adjusting conditions such as the temperature, current density, pH of the plating bath and the like in the electroplating method described later. Specific conditions will be described in detail in the description of the production method below. For example, the temperature of the electroplating method is preferably 20 to 60 ° C., the current density is preferably 1 to 3 A / dm ² , and the alkali component is contained. The conditions which make quantity 40-70 g / L are mentioned.

  The content of the alkali component in the catalyst layer is preferably 50 ppm or more, more preferably 100 ppm or more, and further preferably 150 ppm or more. Since the surface becomes amorphous when the content of the alkali component in the catalyst layer is 50 ppm or more, the hydrogen generation overvoltage can be kept low. Although an upper limit is not specifically limited, Usually, it is preferable that it is 500 ppm or less. The content of the alkali component in the catalyst layer can be measured by ICP after dissolving the electrode.

  Examples of the alkali component include potassium and sodium, and potassium is preferable from the viewpoint of durability and plating stability.

  As the conductive substrate, for example, nickel, nickel alloy, stainless steel, or the like can be used. However, when stainless steel is used in a high-concentration alkaline aqueous solution, considering that elution of iron and chromium and that the electrical conductivity of stainless steel is about 1/10 that of nickel, the conductive base material is Is preferably nickel.

  The shape of the conductive substrate is not particularly limited, and an appropriate shape can be selected depending on the purpose. A plate material, a porous plate, an expanded shape, or a so-called woven mesh produced by knitting a nickel wire is preferable. About the shape of an electroconductive base material, there exists a preferable specification with the distance of the anode and cathode in an electrolytic cell. When the anode and the cathode have a finite distance, a perforated plate or an expanded shape is used. In the case of a so-called zero gap electrolytic cell in which the ion exchange membrane and the electrode are in contact, a woven mesh knitted with a thin line is used. Used.

The manufacturing method of the electrode for hydrogen generation of this invention is demonstrated in detail. The electrode for hydrogen generation of the present invention includes a plating treatment step in which a conductive substrate is plated by an electroplating method using a plating bath containing platinum, and the platinum is electrodeposited from the plating bath on the conductive substrate. Including
The plating bath contains an alkali component in an amount of 40 to 70 g / L, and the temperature of the plating bath during the plating treatment is in a range of 20 ° C to 60 ° C.

  The conductive substrate is preferably roughened in advance. This is because the contact surface area can be increased by roughening, and the adhesion between the conductive substrate and the electrodeposit is improved. The surface roughening means is not particularly limited and can be used by a known method such as sand blasting, etching with oxalic acid or hydrochloric acid solution, washing with water and drying. Moreover, in order to improve the adhesiveness of an electroconductive base material and an electrodeposit, it is preferable to perform base plating beforehand.

  It is preferable that the temperature of a plating bath is 20-60 degreeC, More preferably, it is 20-50 degreeC, More preferably, it is 20-40 degreeC. By setting the temperature of the plating bath to 20 to 60 ° C., the crystallite diameter by X-ray diffraction on the (111) plane of platinum contained in the catalyst layer can be reduced, and the hydrogen generation overvoltage can be kept low.

  The influence of plating on the crystallite diameter can be explained by the kinetics of nucleation and crystal growth. The discharge is not uniformly performed on the entire electrode surface, but the discharge concentrates on the convex portion, and atoms are deposited on that portion. When nucleation, which is atomic precipitation, proceeds preferentially over crystal growth, the crystallite size becomes smaller and microcrystallization occurs. On the other hand, when crystal growth proceeds preferentially over nucleation, the crystallite diameter increases. By lowering the temperature of the plating bath, nucleation proceeds preferentially over crystal growth, and the surface diffusion distance of adsorbed electrons and cations in the plating bath is reduced. Conceivable.

The current density is preferably in a. 1-3A / dm ^2, more preferably 2~2.5A / dm ^2. By setting the current density to 1 to 3 A / dm ² , the crystallite diameter by X-ray diffraction on the (111) plane of platinum can be reduced and microcrystallization can be performed, and the hydrogen generation overvoltage can be suppressed low.

  By increasing the current density, the discharge amount per unit area and time increases, the discharge locations are dispersed due to the influence of space charge, and the convex portions increase. Thus, it is considered that nucleation proceeds preferentially over crystal growth, the crystallite diameter becomes smaller, and microcrystallization occurs.

  The plating bath preferably contains an alkali component. Examples of the alkali component include sodium hydroxide, potassium hydroxide, potassium chloride and lithium hydroxide, and among them, an alkali component containing potassium is preferable.

  The alkali component content in the plating bath is preferably 40 to 70 g / L, more preferably 45 to 65 g / L, and still more preferably 55 to 60 g / L. By setting the alkali component to such a content, the amount of the alkali component in the catalyst layer after plating can be adjusted. 11-14 are preferable, as for pH of a plating bath, More preferably, it is 12-14, More preferably, it is 13-14.

  The plating time, deposition rate, platinum concentration in the plating bath, and the like are not particularly limited, and can be controlled according to the purpose. What is necessary is just to wash | clean the electrode after plating using a pure water or ion-exchange water.

  According to the production method of the present invention, the crystallite diameter by X-ray diffraction on the (111) plane of platinum is 200 mm or less, and the crystal phase existing ratio of the (220) plane and (311) plane of the platinum is 1-15. % Hydrogen generating electrode is obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not restrict | limited to the following example.

Example 1
Conduction of a Ni plate (width 2 cm, height 10 cm) pretreated [sandblast (particle size 150-180 μm), ultrasonically cleaned at room temperature for 1 minute, and electrolytically degreased [treated with 1 M hydrochloric acid for 1 minute] for 30 seconds It was set as a conductive substrate.

Under the following plating conditions, the plating temperature was 30 ° C., and the conductive substrate was plated so that the amount of platinum supported was 10 g / m ² . The SEM image, crystallite diameter, crystal phase existence ratio, ECSA, and electrode potential of the obtained hydrogen generation electrode were evaluated. The results are shown in FIG.

(Plating conditions)
Plating solution: EEJA platinumate 100 with the following changes.
Pt concentration: 20 g / L
Potassium concentration: 55 g / L
pH: 13.8
Deposition rate: 3 minutes / μm ( ^{2.5 A /} dm ² hour)
Plating current density: 2.2 A / dm ²

The crystallite diameter was determined by the X-ray diffraction method using the following formula.
Crystallite diameter: D = Κλ / βcosθ
Κ: Sherler constant (= 0.94)
λ: Wavelength of the X-ray tube used β: Spread of diffraction line depending on crystallite size θ: Diffraction angle

ECSA performed CV measurement (sample electrode measurement area: 10 cm ² ) in a sulfuric acid aqueous solution, and calculated from the electric quantity of a hydrogen atom adsorption wave by the following equation.
ECSA [cm ² / g] = QH [μC] / (210 [μC / cm ² ] × Pt mass [g])
QH: Hydrogen adsorption charge amount 210 μC / cm ² : Adsorption charge amount per unit active area of Pt

Example 2 and Comparative Examples 1-2
Example 1 was repeated except that the plating conditions were changed as described in FIG.

  As can be seen from the results in FIG. 1, the hydrogen generating electrodes of Examples 1 and 2 have a crystallite diameter of 200 mm or less by X-ray diffraction on the (111) plane of platinum, and the (220) plane of the platinum and Since the crystal phase existence ratio of the (311) plane is 1 to 15%, it was suggested that the hydrogen generation overvoltage in alkaline water electrolysis is lower than that of the electrodes of Comparative Examples 1 and 2 that do not satisfy the conditions. Thus, it was found that by using the hydrogen generating electrode of the present invention for alkaline water electrolysis, the electrode activity can be greatly improved and the amount of catalyst can be reduced even at a large current density.

  FIG. 2 shows the result of analysis by the X-ray diffraction method of the electrode produced in Example 1.

  FIG. 3 shows the results of analysis by X-ray diffraction of the electrodes produced in Example 1, Example 2, and Comparative Example 1. Although the presence of each crystal phase of platinum was confirmed at any plating bath temperature, the crystallite diameter of the (111) plane of platinum in the electrode of Comparative Example 1 exceeded 200 mm. This suggests that the hydrogen generation overvoltage in alkaline water electrolysis also increases.

Also, in FIG. 4, electrochemical measurements were performed on the electrodes produced in Example 1, Example 2, and Comparative Example 1 (n = 3). Before electrochemical measurement, electrolytic degreasing, CV potential scanning at 50 mV / s was performed, and the electrode surface was washed each time before use. The measurement conditions are as follows.
As shown in FIG. 4, a low hydrogen generation overvoltage was shown.

(Electrochemical measurement conditions)
Reference electrode: Ag / AgCl
Auxiliary electrode: Pt / Ti
Electrolyte solution composition: 30 wt% KOH aqueous solution Temperature: Room temperature Measurement area: 1 cm ²

Comparative Example 3
The surface of the conductive base material (Ni plate) prepared in Example 1 was brush-coated with a 10% by mass aqueous chloroplatinic acid solution and baked in the air at 500 ° C. for 30 minutes. This operation was repeated about 10 to 15 times, the platinum loading was adjusted to 10 g / m ^2, and the hydrogen generating electrode of Comparative Example 3 was obtained. The SEM image, crystallite diameter, crystal phase existence ratio, ECSA, and electrode potential of the obtained hydrogen generating electrode were evaluated in the same manner as in Example 1. The results are shown in FIG.

Subsequently, a 30% strength by weight potassium hydroxide aqueous solution was heated to 80 ° C., and the electrode of Example 1 (however, the amount of platinum supported was 10 g / m ² ) and the electrode of Comparative Example 3 were immersed for 100 hours. (Each n = 2. That is, electrode 1 and electrode 2 of Example 1, electrode 1 and electrode 2 of Comparative Example 3). The platinum concentration in the aqueous potassium hydroxide solution before and after the immersion was measured by ICP, and the elution amount of platinum into the aqueous solution was examined. The results are shown below.

Elution amount of platinum of electrode 1 of Example 1 = 0.050 mg
Elution amount of platinum in electrode 2 of Example 1 = 0.040 mg
Platinum elution amount of electrode 1 of Comparative Example 3 = 0.512 mg
Platinum elution amount of electrode 2 of Comparative Example 3 = 0.690 mg

  From the above results, the platinum elution amount of the hydrogen generation electrode of Example 1 is about 1/10 or less as compared with the conventional fired electrode produced in Comparative Example 3, and the hydrogen generation electrode of the present invention has the following amount. Proven durability.

  Moreover, the electrochemical measurement of the electrode produced in Comparative Example 3 was performed in the same manner as described above (n = 3). The result is shown in FIG. FIG. 6 is a diagram in which the result (reference numeral 5) of Comparative Example 3 is added to the graph of FIG. As shown in FIG. 6, the electrode of the present invention showed a lower hydrogen generation overvoltage than the conventional fired electrode produced in Comparative Example 3.

FIG. 7 shows the results of analysis by X-ray diffraction of the electrodes produced in Example 1 and Comparative Example 1. As shown in FIG. 7, both the electrode of the present invention (Example 1) and the coated and baked electrode (Comparative Example 3) have greatly different peak intensities although the Pt amount is about 10 g / m ^2. It has been found that the electrode of the invention has a higher Pt catalyst layer having higher crystallinity than the conventional fired electrode as produced in Comparative Example 3, and has high durability.

  In addition, when Example 1 was repeated using the plating bath whose potassium concentration is 40 g / L on the plating conditions of Example 1, it was confirmed that platinum plating was not attached to the electroconductive base material.

Claims (8)

  An electrode for hydrogen generation having a conductive substrate and a catalyst layer formed on the conductive substrate, the platinum containing platinum in the catalyst layer, the X-ray on the (111) plane of the platinum An electrode for hydrogen generation having a crystallite diameter by diffraction of 200 mm or less and a crystal phase existence ratio of (220) plane and (311) plane of platinum of 1 to 15%.   2. The electrode for hydrogen generation according to claim 1, wherein a crystal phase existing ratio of the (111) plane by X-ray diffraction of platinum is 40% or more. The electrode for hydrogen generation according to claim 1 or 2, wherein the platinum has an ECSA (electrochemical activity specific surface area) of 5 m ² / g or more.   The electrode for hydrogen generation according to any one of claims 1 to 3, wherein the content of the alkali component in the catalyst layer is 50 ppm or more.   The electrode for hydrogen generation according to any one of claims 1 to 4, wherein the alkali component is potassium.   It is for alkaline water electrolysis, The electrode for hydrogen generation of any one of Claims 1-5. A method for producing an electrode for hydrogen generation comprising a conductive substrate and a catalyst layer formed on the conductive substrate, wherein the catalyst layer contains platinum.
Plating the conductive substrate by an electroplating method using a plating bath containing platinum, and a plating treatment step of depositing the platinum on the conductive substrate from the plating bath,
The said manufacturing method characterized by the said plating bath containing 40-70 g / L of an alkaline component, and the temperature of this plating bath at the time of this plating process exists in the range of 20 to 60 degreeC.   The method for producing an electrode for hydrogen generation according to claim 7, wherein the alkali component is potassium.