JPH0285385A - Production of electrode - Google Patents

Abstract

PURPOSE:To obtain an electrode for an electrochemical device having low overvoltage and superior durability by regulating the efficiency of deposition of Ni to a specified value or above when Ni plating contg. S is formed on an electrically conductive base material with an Ni plating bath contg. a soluble sulfur compd. to produce an electrode. CONSTITUTION:When Ni plating contg. S is formed on an electrically conductive base material of Fe, Ni, Cr, Cu or an alloy thereof to produce an electrode for an electrochemical device, an aq. soln. contg. a soluble Ni salt such as nickel chloride, nickel sulfate or nickel sulfamate as an Ni ion source and a soluble sulfur compd. such as thiourea or thiocyanate is used as a plating bath and the efficiency of deposition of Ni during plating is regulated to >=95% by increasing the concns. of the Ni salt and the S compd. in the plating bath, adjusting the pH of the bath to about 4 and regulating the temp. of the bath and current efficiency. An electrode having low overvoltage and superior durability is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an electrode, and more specifically, to a method for manufacturing an electrode, and more specifically, to a method for manufacturing an electrode, and more particularly, to a method for manufacturing an electrode, and more specifically, to a sulfur-containing nickel-plated electrode that exhibits low overvoltage characteristics and high durability. It's about manufacturing methods.

The electrode of the present invention can be applied as an electrode in various electrochemical devices, but is particularly suitable for use as an electrode for industrial electrolysis, such as an electrode for water electrolysis or an electrode for salt electrolysis, and has high durability, Moreover, it exhibits extremely low overvoltage characteristics.

[Prior Art] Reduction of electrolysis voltage is an important issue in the field of industrial electrolysis such as water electrolysis and salt electrolysis.

In particular, in cation exchange membrane salt electrolysis technology, which is attracting attention as a new process, various low hydrogen overvoltage cathodes have been developed to reduce the hydrogen overvoltage of the cathode with the aim of reducing electrolysis voltage.

As one of the methods for manufacturing a low hydrogen overvoltage cathode, a method for manufacturing an electrode coated with sulfur-containing nickel by electroplating is already known, and is disclosed in Japanese Patent Publication No. 25-2305 and Japanese Patent Application Laid-open No. 1989-1991 filed by the present inventors. No. 57-19388, No. 57-H4
B78 etc. have been proposed.

These electrodes having a sulfur-containing nickel plating coating can be obtained by an economical method, and some examples have already been put into practical use. However, conventional sulfur-containing nickel-plated electrodes exhibit low hydrogen overvoltage characteristics at the initial stage of electrolysis, but have the disadvantage that they gradually deteriorate over time and the overvoltage increases; for example, in salt electrolysis. In the field of industrial electrolysis, the life is 2~
It was a short period of 3 years.

[Problems to be Solved by the Invention] The purpose of the present invention is to propose a method for manufacturing a low overvoltage electrode that exhibits excellent durability with low overvoltage and little deterioration regarding sulfur-containing nickel plated electrodes. be.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventors have conducted extensive studies regarding sulfur-containing nickel-plated electrodes, particularly regarding the plating conditions and the electrode characteristics of the resulting electrodes. The present inventors have discovered that an electrode obtained with a nickel deposition efficiency of 95% or more during plating exhibits an extremely low overvoltage and has excellent durability with little deterioration, leading to the completion of the present invention. That is, the present invention provides a method for producing an electrode in which nickel plating containing sulfur is applied on a conductive substrate using a nickel plating bath containing a soluble sulfur compound.
This method of manufacturing an electrode is characterized by performing nickel plating under conditions such that the output efficiency is 95% or more.

Nickel plating containing sulfur in the present invention can be performed by electroplating from a nickel plating bath containing a nickel salt and a soluble sulfur compound having an oxidation number of 5 or less. This plating reaction is carried out through several elementary reaction steps, and although the details have not been fully elucidated, the result is that sulfur and nickel are eutectoid. The nickel deposition efficiency that characterizes the present invention refers to the percentage of the plating electricity that is deposited in the coating, assuming that Ni 2"4 in the plating bath is deposited as Ni on the electrode base material by a two-electron reaction. It is a numerical value that represents the amount of nickel used in the precipitation of nickel contained in
A H1 mole) Nickel m in the film: W (Durham) Nickel molecule m: Wo (58.7 grams 1 mole)
Nickel precipitation efficiency: When η is (η/100) X (Q/2F) −W/W.

Therefore, it can be defined as 77-2 FW X 100 / Q W □.

Here, nickel precipitation efficiency of 95% or more means that
This means that most of the plating electricity is ultimately used for nickel deposition, and the other plating electricity is used, for example, for reactions of sulfur compounds, hydrogen generation reactions, and the like.

An electrode obtained by applying nickel plating under conditions where the nickel precipitation efficiency is 95% or more maintains an extremely low overvoltage for a long period of time, resulting in an electrode with low overvoltage and high durability. The reason for this is not clear, but it is thought that most of the electrical charge is used for nickel deposition, suppressing other reactions, and as a result, an active, highly dispersed state of nickel and sulfur is achieved. It will be done.

The nickel precipitation efficiency during plating changes depending on the plating conditions. According to studies by the present inventors, the nickel precipitation efficiency increases as the nickel salt concentration and sulfur compound concentration in the plating bath increases. Also, a decrease in plating current density, an increase in pH, and an increase in temperature increase the nickel deposition efficiency. Therefore, by appropriately understanding this relationship and appropriately changing the plating conditions, it is possible to perform sulfur-containing nickel plating under conditions where the nickel precipitation efficiency during plating is 95% or more.

As an example of a preferable plating condition range, using a plating bath with a nickel ion concentration of Q, 5-3.0 sol/I, and a soluble sulfur compound concentration of 0.3-1.0 iol/I,
While maintaining the pH of the plating bath in the range of 2.5 to 6.0, the current density during plating was set to 0.1 to 3. Examples include conditions for setting OA/d112.

The nickel plating bath used in the present invention contains a soluble nickel salt such as nickel chloride, nickel sulfate, or nickel sulfamate, and a soluble sulfur compound. As the soluble sulfur compound, for example, a thiocyanate, a thiourea, or an oxyacid salt having a sulfur oxidation number of 5 or less, such as a salt of sulfite, bisulfite, thiosulfate, dithionite, etc. can be used. Among these, it is desirable to use thiourea in order to increase the nickel precipitation efficiency.

Furthermore, as already proposed by the present inventors, one of the preferred methods is to add ammonia ions to the nickel plating bath to obtain an active nickel plating film that is strong and exhibits excellent durability.

Examples of the conductive base material used in the present invention include metals, conductive resins, ceramics, and other conductive base materials. , from the mechanical and chemical durability of the group H and economic efficiency, it is preferable to use iron, nickel, chromium, copper, or an alloy thereof. The shape of the conductive base material may be any shape such as a flat plate, mesh shape, porous shape, etc., but when used as a gas generating electrode at high current density, it may be in the shape of an expanded metal, punched metal, wire mesh, etc. It is preferable to use a shaped one.

Furthermore, in the method for manufacturing an electrode of the present invention, these conductive substrates may be subjected to appropriate pretreatment.

Appropriate pretreatments include, for example, strike nickel plating using a hydrochloric acid acidic nickel plating bath, which is known as a method for removing passive films on stainless steel surfaces, or ordinary nickel plating applied to improve the corrosion resistance of iron base materials, or Refers to base nickel plating that exhibits excellent adhesion to both the base material and sulfur-containing nickel plating. Of these, the base nickel plating also serves to improve the durability of the resulting electrode. One preferable example of base nickel plating is to form a special nickel plating layer exhibiting an orientation of (111)/(200)≧1.

Such special base nickel plating not only has excellent adhesion with conductive substrates, but also shows extremely excellent adhesion with activated nickel plating, and the resulting electrodes have excellent adhesion. This results in a low overvoltage electrode that exhibits excellent durability.

The orientation of (Ill)/(200)≧1 is defined by the X-ray lp1 constant of the nickel plating film, and the diffraction characteristic of the X-ray a+++ constant is + -) to (111).
It means that the intensity of the (200) peak is read and the ratio is (111)/(200)≧1. That is, a special nickel plating film exhibits orientation in the (111) plane.

[Examples] Examples of the present invention will be described below, but the present invention is not limited thereto.

Example 1 Comparative Example 1 As Example 1, the following electrode samples were produced. 1ffl m of acrylic resin surrounding the conductive base material
A 1Oφ nickel disk with only the surface exposed was used. After normal pretreatment such as degreasing and pickling, a base nickel plating film is formed using the nickel plating bath and plating conditions shown in Table 1, and then on top of that, using the nickel plating bath and plating conditions shown in Table 2. An electrode was manufactured by forming a sulfur-containing nickel plating film.

The base nickel plating exhibited an orientation with a (1,11)/(200) ratio of approximately 2.8, and the nickel precipitation efficiency of the sulfur-containing nickel plating was 100%.

Table 1 Base nickel plating conditions Plating bath composition> - Nickel chloride/ammonium chloride plating conditions> - Current density, temperature, pH - Plating time 1.2 mol/1 1.5 mol/1 2, OA/d112 40°C 4. 0 0.5 hours Table 2 Nickel plating conditions containing sulfur and plating bath composition> - Nickel chloride 1.2 mol/tothiourea
0.4 mol/1 ・Ammonium chloride l, Omol/1 plating conditions> ・Current density L, QA/d+*2 ・Temperature 60°C ・pH 4.0 ・Plating time 4 hours On the other hand, as Comparative Example 1, sulfur was An electrode was produced under the same conditions as in Example 1, except that the nickel plating conditions included were as shown in Table 3. In addition, the Ni-Sokel precipitation efficiency of Comparative Example 1 was 91%.
Met.

Table 3 Nickel plating conditions including sulfur plating bath composition> Nickel chloride 0.5 mol/tothiourea
0.3mol/1 ・Ammonium chloride plating conditions> ・Current density 4. OA/di2 ・Temperature 60℃ ・pH 4.0 ・Plating time 1 hour 1.0 Ilol/I This Example 1. Each sample electrode of Comparative Example 1 was made of 32% Na by weight.
Water electrolysis tests were carried out in OH solution and used as a cathode. A nickel anode was used as the anode, and the current density during electrolysis was 400 A/d+a 2 . The electrolysis was interrupted every appropriate amount of electrolysis electricity, and the electrolysis was carried out at 4OA/d in a 32% NaOH solution at 90°C, which is an example of the conditions for normal salt electrolysis.
The hydrogen overpotential was measured at a current density of a2.

The results are shown in FIG. In Figure 1, 40^ld is on the vertical axis.
The hydrogen overvoltage in m2 is shown, and the horizontal axis is 400A/d112
Shows the electrolysis time at From FIG. 1, it can be seen that the electrode obtained in Example 1 of the present invention has excellent durability with little deterioration over a long period of time.

Example 2 As Example 2, an electrode was produced under the same conditions as Example 1, except that the sulfur-containing nickel plating conditions were changed.

Table 4 shows the sulfur-containing nickel plating conditions. In addition,
The concentration of nickel chloride in the nickel plating bath is 0.1 to 2.
Plating was performed by changing it to 0Illol/I.

Table 4 Nickel plating conditions containing sulfur plating bath composition> - Chive chloride, Kel 0.1-2.0 01/Stone urinary chord 0 Jsol/I - Ammonium chloride 1. On+ol/I plating conditions> ・Current density 2. OA/d+a2 ・Temperature 60℃ ・I) H4,0 ・Plating time 2 hours In Figure 2, the horizontal axis shows the nickel chloride concentration in the plating bath, and the vertical axis shows the nickel precipitation efficiency during plating and 40OA/d.
Hydrogen overvoltage after electrolysis at m2 for 10 days (90℃
, 32 wt% NaOH solution, 40 A/dm 2). The nickel deposition efficiency increases as the nickel chloride concentration increases, but when the nickel deposition efficiency exceeds 95%, it is clear that an electrode that maintains a low overvoltage even after electrolysis at 400 A/di 2 for IO days has been obtained. Recognize.

Example 3 As Example 3, an electrode was created under the same conditions as Example 1 except that the sulfur-containing nickel plating conditions were changed. Table 5 shows the sulfur-containing nickel plating conditions. In addition, the current density during nickel plating is 0.25 to IOA/ds.
I changed it to 2 and performed the plating.

Table 5 Nickel plating conditions including sulfur plating bath composition> - Nickel chloride 1. Omol/1φthiourea
0.3mol/1・Ammonium chloride 2.0 mouths/1 plating condition>・Current density 0.25~IOA/d+e2 Pot temperature
60°C ・pH 4 ・Plating time 2 hours In Figure 3, the horizontal axis shows the current density in the plating bath, and the vertical axis shows the nickel precipitation efficiency during plating and 400 A/dm 2
Hydrogen overvoltage after electrolysis for 10 days (90℃).

32% by weight NaOH solution, 40A/da'').

Although the nickel deposition efficiency increases with decreasing current density,
When the nickel precipitation efficiency is 95% or more, 400A/d
It can be seen that an electrode was obtained that maintained a low overvoltage even after electrolysis at m2 for 10 days.

Example 4 As Example 4, a 14 cm x 14 cm nickel expanded band metal (minor axis 7 ha, major axis 1
2.7a+m) to perform usual pretreatment such as degreasing and pickling, and then apply a base nickel plating film and a sulfur-containing nickel plating film by the method shown in Example 1 to produce a low overvoltage electrode.

This electrode is used as a cathode, and a fluorine-based cation exchange membrane (Nafion DuPont product name) is used as an anode.
Salt electrolysis was carried out under the electrolytic conditions shown in Table 6 using a DSA type expanded metal having a Ru T t O 2 coating on Ti.

Table 6 Salt electrolysis conditions Anode chamber NaC1 concentration 230g/l Cathode chamber Na011 concentration -32 heavy ffi, %Na0i1
Current density: 40 A/da" Temperature: 90°C Distance between positive and cathode: 2■ During two years of electrolytic operation, the hydrogen overvoltage of the low overvoltage electrode obtained by the present invention is almost constant at 140n+v to 160a+v, and the electrolytic voltage is also 3. The voltage was almost constant at .15 to 3.20V.

Reference Example The deterioration behavior of a nickel-plated electrode containing sulfur shows a capacitance factor-dependent deterioration behavior over time.

An example is shown in FIG. This figure shows an example of using one of the sulfur-containing nickel-plated electrodes as a hydrogen generating cathode for water electrolysis. The anode uses a nickel plate,
Electrolysis was carried out in a 2% by weight NaOH solution. The current density during electrolysis was varied from 4OA/dm'' to 400A/dm2, and the fu solution was interrupted at each appropriate amount of electrolyzed electricity.
Hydrogen overpotential was measured at a current density of 40 A/dg 2 in fm% NaOH solution.

Based on these experiments, the inventor discovered that sulfur-containing nickel plating was done! ! ! It has been found that the deterioration behavior of electrodes depends on the amount of electricity electrolyzed, regardless of the current density during electrolysis (as the current density changes, the overvoltage changes).

FIG. 4 is a diagram showing the deterioration behavior of an example of a conventionally proposed electrode, and it can be seen that the hydrogen overvoltage increases with the amount of electrolyzed electricity. Thus, the sulfur-containing nickel-plated M1 electrode exhibits a capacitive factor-dependent deterioration behavior over time. Therefore, the performance of a sulfur-containing nickel-plated electrode can be evaluated by an accelerated test method with increased current density. That is, Example 1
~31; The electrolysis of 400 A/d++'' shown here indicates that the electrolysis is carried out under conditions accelerated by 10 times compared to the electrolysis of 40 A/d-, like the cathode of normal salt electrolysis.

[Effects of the present invention] The present invention provides conditions under which the nickel precipitation efficiency during plating is 95% or more when applying sulfur-containing nickel plating that exhibits low overvoltage characteristics on a conductive substrate using an electroplating method. The present invention proposes a method of manufacturing an electrode characterized by applying the nickel plating.

The electrode according to the present invention can be used as an electrode in various electrochemical devices, but is particularly suitable for use as an electrode for industrial electrolysis, such as an electrode for water electrolysis or an electrode for salt electrolysis, and is highly durable. It exhibits very low overvoltage characteristics, making it possible to reduce the electrolytic voltage by several LOOmv over a long period of time, and its industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 shows Example 1. 3 is a diagram showing the overvoltage after electrolysis of the cathode obtained in Comparative Example 1. FIG. FIG. 3 is a diagram showing the current density in the plating bath, the nickel deposition efficiency during plating, and the overvoltage after electrolysis of the obtained electrode in Example 3. FIG. 4 is a diagram showing the deterioration behavior of a nickel-coated electrode containing sulfur.

Claims (1)

[Claims] (1) In an electrode manufacturing method in which nickel plating containing sulfur is applied on a conductive substrate using a nickel plating bath containing a soluble sulfur compound, nickel plating is performed under conditions such that the nickel precipitation efficiency is 95% or more. A method for manufacturing an electrode characterized by: