JP2015178666A - Alloy electrode for hydrogen generation and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alloy electrode for hydrogen generation having high activity to hydrogen generation when used for electrolysis of an alkali aqueous solution and a manufacturing method therefor.SOLUTION: There is provided an alloy electrode manufactured by forming alloy having composition containing iron:45 to 65 atom% and carbon:0.6 to 10 atom%, the balance 5 atom% or more of nickel and 0.1 atom% or more cobalt on an appropriate electrode substrate. The alloy electrode is manufactured by conducting electrolysis with using a plating liquid containing soluble salt of cobalt, soluble salt of nickel, amino carboxylic acid and boric acid and adjusted pH to 2 or less by adding acid and depositing Fe-Co-Ni-C alloy on a cathode base material.

Description

The present invention relates to an alloy electrode for electrolyzing an alkaline aqueous solution to generate hydrogen and a method for producing the same. The electrode of the present invention can generate hydrogen at a high rate when it is used for electrolysis of a hot, neutral or strongly alkaline aqueous solution.

In order to use renewable energy, technologies such as solar power generation and wind power generation are being developed, but the problem with the power derived from these renewable energy is that the amount of generated power fluctuates every moment. Or to be intermittent. As one measure for coping with this problem, it has been studied that water is electrolyzed using the electric power, in particular, electrolysis of an alkaline aqueous solution to produce hydrogen to serve as an energy source. In order to efficiently perform electrolysis, a cathode and an anode in which electrolysis of an aqueous solution proceeds with low power consumption is required, and a technique for manufacturing such an electrode is being developed.

One of the inventors, together with other co-inventors, invented a highly active and durable alloy electrode for hydrogen generation, and the electrodeposition is a simple and low cost electrode manufacturing technique. Invented a method that uses the law and disclosed it at an early stage (Patent Document 1). The alloy electrode for hydrogen generation contains iron: 2.9 to 45 atomic% and carbon: 0.6 to 10 atomic%, with the balance being 5 atomic% or more nickel and 0.1 atomic% or more cobalt. It is an electrode formed on the surface of an appropriate electrode base material using an alloy having an occupied composition as an electrode active material. This method of producing an alloy electrode for hydrogen generation includes an oxycarboxylic acid or an aminocarboxylic acid in addition to a soluble salt of iron, a soluble salt of cobalt, and a soluble salt of nickel, and an acid is added to reduce the pH to 2 or less. Electrolysis is performed using the adjusted plating solution, and the Fe—Co—Ni—C alloy is deposited on the cathode base material.
Japanese Patent No. 4561149

The iron content in the alloy electrode of Patent Document 1 is 2.9 to 45 atomic%, but this upper limit is that when a large amount of Fe is added to the Ni—Co alloy, the crystal structure of the alloy is changed from the face-centered cubic crystal. It is determined from the fact that it changes to a body-centered cubic crystal and Fe is easily dissolved from the electrode when electrolysis is interrupted, and the durability of the electrode is impaired. However, this problem can be largely avoided by adjusting the use conditions of the electrode, and is not fatal until the iron content exceeds 65 atomic%. Subsequent studies have shown that the presence of more than 45 atomic% iron results in higher activity against hydrogen generation.

An object of the present invention is to utilize the newly obtained knowledge and provide an alloy electrode that is used for electrolyzing an aqueous solution to generate hydrogen and exhibiting high activity. It is also within the scope of the present invention to provide a method for manufacturing this alloy electrode.

The alloy electrode for hydrogen generation of the present invention comprises a metal electrode base material containing iron: more than 45 atomic% and 65 atomic% or less and carbon: 0.6-10 atomic%, with the balance being 5 atomic% or more. It is an electrode formed by coating with an alloy having a composition of nickel and 0.1 atomic% or more of cobalt.

The method of the present invention for producing the above-described alloy electrode for hydrogen generation contains aminocarboxylic acid and boric acid in addition to soluble salt of iron, soluble salt of cobalt and soluble salt of nickel, and pH is adjusted by adding acid. Using a plating solution of 2 or less, electrolysis is performed using a metal electrode substrate as a cathode, and an Fe—Co—Ni—C alloy having the above composition is deposited on the electrode substrate. Adding a small amount of an additive such as sodium dodecyl sulfate to this plating solution is also effective in improving the smoothness of the surface of the resulting electrode.

In the alloy electrode for hydrogen generation of the present invention, a nickel component is essential in order to prevent corrosion dissolution during natural immersion in an alkaline aqueous solution for electrolysis, but in order to improve the activity against hydrogen generation, iron, cobalt And need to contain carbon. Among them, it has been confirmed that an alloy containing a large amount of iron in the vicinity of 50 atomic% or more together with carbon and cobalt has particularly high hydrogen generation activity. Thus, the electrode of the present invention is an electrode for generating hydrogen by using it in electrolysis of an alkaline aqueous solution, and has both high activity and excellent durability.

According to the method for producing an alloy electrode for hydrogen generation of the present invention, an alloy having a desired composition can be obtained by a simple method called electroplating, and a high-performance electrode can be produced at a low production cost.

Hereinafter, the reason why the composition of the alloy forming the hydrogen generating electrode of the present invention is limited as described above will be described.
Fe: more than 45 atomic% and not more than 65 atomic% Iron is an element having an action of accelerating the discharge of hydrogen on cobalt and nickel, and has high activity against hydrogen generation by coexisting with carbon in the electrode alloy. Is granted. It is disclosed in Patent Document 1 that an iron content of 2.9 to 45 atomic% in the alloy is useful for this purpose. However, an alloy exceeding 45 atomic% has high activity for hydrogen generation. On the other hand, if a large amount of iron is added to the Ni—Co alloy, iron is easily dissolved when the electrolysis is interrupted, and the durability of the electrode is lowered. Therefore, it is necessary to stop the addition of iron to 65 atomic% or less.

C: 0.6 to 10 atomic%
Carbon combines with these metal elements in the Fe-Co-Ni alloy, accelerates the discharge of hydrogen by charge transfer and improves the activity against hydrogen generation, and the metal elements are corroded and dissolved when electrolysis is stopped. It has the effect | action which prevents. In order to exert this effect, 0.6 atomic% or more of carbon must be present in the alloy. However, if added in excess, the iron carbide phase is separated from the face-centered cubic parent phase, and instead causes iron to dissolve when the electrolysis is interrupted, so it must be made 10 atomic% or less.

Co: 0.1 atomic% or more excluding 5 atomic% or more occupied by nickel in the balance, cobalt is an element that increases the hydrogen generation ability of the alloy when coexisting with nickel. It is necessary to be present at 0.1 atomic% or more.

Ni: Of the balance, 5 atomic% or more excluding 0.1 atomic% or more occupied by Co is an essential element for the alloy of the present invention, and gives high activity against hydrogen generation. On the other hand, if the electrolysis is interrupted when the electrode is used, the Co—Fe-based alloy is easily corroded in the aqueous solution.

In the method for producing an alloy electrode of the present invention, a preferred example of the aminocarboxylic acid added to the plating bath is lysine (C ₆ H ₁₄ N ₂ O ₂ ). Lysine may be used in the form of hydrochloride (C ₆ H ₁₄ N ₂ O ₂ · HCl · HCl). The alloy forming the electrode of the present invention may contain a small amount of sulfur and phosphorus mainly derived from impurities in the raw material, but there is no hindrance to activity against hydrogen generation or durability.

[Example 1]
Prepare an aqueous solution with the following composition:
NiSO ₄ · 6H ₂ O 1.14 mol NiCl ₂ · 6H ₂ O 0.19 mol CoSO ₄ · 7H ₂ O 0.001 mol FeSO ₄ · 7H ₂ O 0.108 mol H ₃ BO ₃ 0.49 mol C ₁₂ H ₂₅ NaSO ₄ 0.104 mmol C ₆ H ₁₄ N ₂ O ₂ HCl 0.125 or 0.2 molar sulfuric acid was added to adjust the pH to 1.5 to obtain a plating bath.

Using this plating bath, an electrode was manufactured by plating on a nickel substrate at a current density of 500 A / m ² for 18 minutes under the condition of an electric quantity of 540 kC / m ² . Using the obtained electrode, electrolysis was performed at 90 ° C. in a 30 wt% KOH aqueous solution at a constant current, and a constant current polarization curve of hydrogen generation was measured. The Tafel slope of the polarization curve was as low as about 36 mV / decade, indicating the highest activity that could be realized mechanistically. The composition of the obtained electrode and the value of hydrogen generation overvoltage at a current density of 1,250 A / m ² are shown in Table 1 below. For comparison, the data of the electrode of Patent Document 1 and the electrode containing no carbon in the electrode active material are also shown.

Table 1

[Example 2]
An aqueous solution having the following composition was prepared. This is a one-digit higher cobalt salt concentration than the composition of Example 1.
NiSO ₄ · 6H ₂ O 1.14 mol NiCl ₂ · 6H ₂ O 0.19 mol CoSO ₄ · 7H ₂ O 0.01 mol FeSO ₄ · 7H ₂ O 0.108 mol H ₃ BO ₃ 0.49 mol C ₁₂ H ₂₅ NaSO ₄ 0.104 mmol C ₆ H ₁₄ N ₂ O ₂ HCl 0.1-0.4 mol sulfuric acid was added to adjust the pH to 1.5. Using this plating solution, a nickel substrate was plated with a current density of 300 A / m ² and an electric quantity of 180 kC / m ² under the conditions of 10 minutes to produce an electrode for hydrogen generation.

Using the obtained electrode, electrolysis was performed at 90 ° C. in a 30 wt% KOH aqueous solution at a constant current, and a constant current polarization curve of hydrogen generation was measured. Similarly to the electrode of Example 1, the electrode of Example 2 had a low Tafel slope of the polarization curve for hydrogen generation of about 36 mV / decade, and exhibited the highest activity that could be realized in terms of reaction mechanism. The composition of the obtained electrode, the value of the hydrogen overvoltage at a current density of 1,250A / m ^2, given in Table 2 below. The data of the comparative example is also shown for convenience of reference.

Table 2

The electrode of the present invention exhibits a hydrogen generation overvoltage equivalent to or lower than that of the electrode of Patent Document 1, and can realize energy saving suitable for use for the purpose of generating hydrogen by electrolyzing a concentrated alkaline aqueous solution at a high temperature. The cathode.

Claims (2)

A metal electrode base material containing iron: more than 45 atomic% and 65 atomic% or less and carbon: 0.6-10 atomic%, with the balance being 5 atomic% or more nickel and 0.1 atomic% or more cobalt An alloy electrode for hydrogen generation formed by coating with an alloy having a composition occupied by. A method for producing an alloy electrode for hydrogen generation according to claim 1, comprising a soluble salt of iron, a soluble salt of cobalt, a soluble salt of nickel, an aminocarboxylic acid and boric acid, and the pH is adjusted by adding an acid. A production method comprising using a plating solution of 2 or less, performing electrolysis using a metal electrode substrate as a cathode, and precipitating a Fe—Co—Ni—C alloy on the electrode substrate.