JPS63179094A - Pr plating method - Google Patents

Abstract

PURPOSE:To form a PR plating exhibiting high durability and a low hydrogen overvoltage characteristic by forming the coated film of an alloy of the surface of an electrically conductive base material by a cathode current in a soln. of the salt of a noble metal and the salt of a base metal, and dissolving and removing the base metal in the coated film by an anode current. CONSTITUTION:The soln. of at least one kind of salt selected from the salts of noble metals and at least one kind of salt selected from the salts of base metals is prepared. The coated film of the alloy of the noble metal and the base metal is formed on the surface of the conductive base material by a cathode current in the soln. by using a PR plating method. The base metal in the alloy coated film is then selectively dissolved and removed by an anode current. For example, Zn is removed from an Ni-Zn eutectoid coated film. By this method, a Raney alloy activating electrode, etc., exhibiting high durability and a low electrochemical over-voltage can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electroplating method, and in particular, an alloy film is formed by a cathodic current, and a base metal is selectively dissolved and removed by an anode current. This relates to a PR plating method characterized by repeated operations.

The plating film obtained by the present invention can be used in a wide range of applications, from corrosion-resistant steel plates to catalysts, depending on its alloy composition. In particular, a feature of the plating film according to the present invention is that a type of metal generally referred to as a Raney catalyst can be easily obtained, and it is suitable for use as a catalyst. Furthermore, as an example of catalytic application, when used as an electrode, it can be applied as an electrode in various electrochemical devices such as an electrode for oxygen/hydrogen generation, an electrode for fuel cells, etc. In particular, it can be used as an electrode for industrial electrolysis, For example, it is suitable for use as a cathode for water electrolysis or salt electrolysis, and is durable.

It has excellent adhesion and exhibits extremely low hydrogen overvoltage characteristics.

[Conventional technology]

The electrodeposit obtained by the plating method of the present invention can be used in a wide range of applications as mentioned above, but among these, it is most likely to be used as a catalyst, especially as an electrode for water electrolysis or salt electrolysis. Bring it up and mention it.

Raney alloys used as general catalysts are mainly Ni-Al, Ni-Zn alloys, etc. obtained by metallurgical methods. In this case, it is necessary to remove Al and Zn by dissolving Kl and Zn in an alkaline solution such as a caustic soda bath solution.

Regarding use as an electrode, it is suitable for use as an electrode for water electrolysis and salt electrolysis, but in these fields,
Reducing electrolysis voltage has become an important issue. In particular, in the field of cation exchange removal salt electrolysis technology, vigorous studies have been carried out in various places to reduce the hydrogen overvoltage (around 14 V) of conventional iron cathodes.Production of low hydrogen overvoltage cathodes As a method (i, +1) A method of performing nickel plating using a nickel plating bath containing a sulfur-containing compound (Japanese Patent Application Laid-Open No. 57-19388
No. etc.).

(2) A method for obtaining an activated electrode from a Raney nickel type electrodeposit is to electrodeposit a Ni-Zn alloy and then immerse it in an alkaline solution, or electrolyze it as an anode in an alkaline or mineral acid solution. , a method for eluting and removing zinc and other soluble substances (Japanese Patent Publication No. 51-6611, etc.).

etc. have been proposed.

These proposed cathodes can be obtained by economical methods, and some exhibit relatively low hydrogen overpotentials at the initial stage of electrolysis.
Although it is considered promising as a low hydrogen overvoltage cathode, it has the disadvantage that the hydrogen overvoltage gradually increases as the number of days of electrolysis increases, and this tendency becomes more pronounced as the electrolytic current density used as the cathode increases. In particular, the so-called electrodeposited Raney nickel type low hydrogen overvoltage cathode, which is made by removing zinc from a nickel-zinc eutectoid coating, has a structure in which the coating layer itself is
The problem was that it was brittle and had poor durability.

[Problems to be solved by the present invention]

The present invention is a PR plating method that provides a new method for producing Raney catalysts, and provides a method for producing special Raney catalysts laminated in multiple layers by an economical and simple method. For example, by using a nickel-zinc eutectoid coating, which has conventionally had durability problems, a new type of activated electrode that exhibits high durability and extremely low electrochemical overvoltage has been developed. A Raney alloy activated electrode can be obtained.

[Means to solve the problem]

The gist of the present invention is to use a PR plating method in a bath solution in which at least one salt selected from noble metals and at least one salt selected from base metals are dissolved on the surface of a conductive base material. The cathode current forms an alloy film of at least one metal selected from noble metals and at least one metal selected from base metals, and the anode current selectively removes the base metal in the alloy film. The PR plating method is characterized by repeating the operation of dissolving and removing the particles.

The combination of a noble metal and a base metal must be a combination that causes abnormal eutectoid formation. Anomalous eutectoid is a phenomenon in which base metals precipitate preferentially compared to noble metals. Such metal combinations include Fe-Ni, Fe-Co,
Zn-iron group system, Ca-iron group system, etc. are known, but
The combination is not limited to this as long as it shows abnormal eutectoid.

In the alloy compositions shown above, the metals shown on the left are base metals, and the metals shown on the right are noble metals. The present inventors have found that these eutectoid coatings can be normally dissolved, that is, selective KW dissolution of base metals, in the same bath as the eutectoid bath by selecting appropriate anode dissolution conditions. Furthermore, the present invention was completed by repeating abnormal eutectoid and normal dissolution using the PR plating method.

The pulse plating method, including the PR plating method, is a generally widely known plating method, and its purpose is to improve uniform electrodeposition, leveling, and increase the plating speed. An example for selective dissolution of
Never existed.

The present inventors have conducted intensive studies on abnormal eutectoid in pulse plating methods, especially PR plating in which the current is periodically reversed, and have found that by setting appropriate pulse conditions, abnormal eutectoid We discovered for the first time that it is possible to repeat normal dissolution, that is, selective dissolution of base metals, and this allows us to achieve the characteristics of uniform electrodeposition and improved leveling originally found in the pulse plating method, while reducing the amount of base metals ( We have now completed a plating method to obtain an alloy film with a multilayer structure in which a portion of the metal is selectively dissolved.The present invention provides a multilayer Raney catalyst with special and excellent functions.
When this is applied as an electrode for industrial electrolysis, especially as a cathode for water electrolysis or salt electrolysis, it is an active Raney alloy with a multilayer structure that exhibits excellent uniformity, adhesion, and durability, as well as extremely low hydrogen overvoltage. It is possible to obtain a chemical electrode.

As the conductive base material used in the present invention, any conductive base material such as metal, conductive resin, or ceramics can be used, but in the case of a hydrogen generating electrode using an alkaline water bath such as salt electrolysis, , iron, nickel, chromium, copper, or an alloy thereof.

Furthermore, the shape of the electrode substrate may be any shape such as a flat plate, a mecca shape, a porous shape, etc., but when used as a gas generating electrode at high current density, it is particularly suitable for use in the shape of expanded band metal, punched metal, wire mesh, etc. Preferably, a base shape is used.

The plating bath used in the present invention contains, as essential components, at least one kind of salt that belongs to noble metals and at least one kind of salt that belongs to base metals.
Usually, any salt such as chloride salt, sulfate salt, sulfamate salt, etc. is used.

Further, the bath temperature of one plating bath can be arbitrarily selected, but the plating is usually carried out in a range from room temperature to 100°C. In addition, in order to obtain a good electrodeposit, it is necessary to
A bath temperature of 0°C is preferred.

The cathode current density can be selected at any value within the range in which abnormal eutectoid deposition occurs, but it is usually carried out in the range of α5 to 50 A/-. Moreover, the cathode electrolysis time in one cycle of dissolution deposition can be selected at any value.
It can usually be carried out within a range of 30 minutes to 1 second.

Although an arbitrary value can be selected for the anode current density, the anode current density is usually Q in the range of 5 to 50 A/-. Further, the anode electrolysis time in one cycle of dissolution deposition can be selected to be any value, but it can usually be carried out within a range of 30 minutes to 1 second.

Furthermore, any value can be selected for the total plating time, but when used as an active cathode, the plating film thickness is usually 10~! The plating time may be selected so as to fall within the range of 1001IrrL.

In the PR plating method of the present invention, selective dissolution of base metals is performed by periodic anodic dissolution in the same bath as the eutectoid bath. Values and times need to be adjusted appropriately depending on the given cathodic electrolysis conditions. By monitoring the potential during anode dissolution, it is observed that the dissolution potential increases from the dissolution potential of a base metal to the dissolution potential of a noble metal, so the conditions necessary for dissolution can be estimated relatively easily. . - As an example, in Figure 2 N1(1!'l,:
ZnO14:NH, C1-1: (L5: 1 [
M], in a bath at 25° C., after eutectoid deposition for 1 minute at a density of 4 A/di, and then flow-tight in the same room.

The results are shown when the anode is melted at 30°C. (A in Figure 2)
The potential up to one point indicates the dissolution of Zn. Therefore (A)
It is sufficient to stop the dissolution at this point. The anodic electrolysis conditions are as follows:
It is effective to choose a method in which base metals are selectively dissolved, but the same effect may be obtained even if some noble metals are melted at the same time.

Once the anodic electrolytic conditions corresponding to any cathodic electrolytic conditions have been determined in this way, by periodically repeating the process, at least one metal selected from noble metals and one selected from base metals can be combined. An electrodeposited material in which the base metal in the alloy coating is selectively dissolved and removed can be obtained from an alloy coating with at least one type of metal.

[Effects of the present invention]

The present invention provides a novel method for obtaining metals of the type commonly referred to as Raney catalysts by electroplating. The plating film obtained by the present invention can be used in a wide range of applications, from corrosion-resistant steel plates to catalysts, depending on its alloy composition. This type of metal is readily available and suitable for application as a catalyst. As an example of catalytic application, when used as an electrode, it can be applied as an electrode in various electrochemical devices such as an electrode for oxygen/hydrogen generation, an electrode for a fuel cell, etc., but it is particularly applicable as an electrode for industrial electrolysis, e.g. When applied as a cathode for water electrolysis or salt electrolysis, it has excellent durability and adhesion, and can reduce hydrogen overvoltage by several hundred mV for a long period of time, and its industrial value is extremely large. be.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Examples 1 and 2. Comparative Example 1 was used as a polar base material, and a nickel base material with a diameter of 1 cM was used, and the periphery thereof was covered with an acrylic resin. After pretreatment such as degreasing and pickling, and base plating, Table 1.2
PR plating was performed under the plating solution composition and electrolytic conditions including the nickel salt and zinc salt shown in . Here, Table 1 shows the plating solution composition and tM conditions of Example 1, and Table 2 shows the plating solution composition and electrolysis conditions of Example 2. Further, as a comparative example, Table 3 shows the plating solution composition and electrolytic conditions of an example of a Ni-Zn alloy in which the conventional PR pulse method was not used.

The electrode performance was evaluated using a hydrogen generation reaction at 40 A/- at 90° C. using a 55 wt*NaOH water bath solution as the electrolyte. For the reference electrode, the same solution as the electrolyte (same pH),
Reversible hydrogen electrodes at the same temperature (hereinafter abbreviated as R, T (J))
was used. A current interrupter method was used to measure the electrode potential to eliminate voltage drops due to solution resistance. In addition, in the hydrogen generation reaction, R, HoE.

The hydrogen overvoltage is the absolute value of the electrode potential measured using the standard.

Table 1 Plating solution composition and electrolytic conditions of Example 1 Plating solution composition Electrolytic condition N1 (J, 1.0m0171 K solution temperature ・
25℃ZnC1,Q,5! nol/1pH4NH
4C11,0mol/1 Cathode current 1o
&a/Anode current 6.5A/di Sword pulse width 60 seconds Anode pulse width 60 seconds Electrolysis time 60 minutes Table 2 Plating solution composition and electrolytic conditions of Example 2 Plating solution composition Electrolytic conditions N i C1@1. Om O1/1 Electrolysis temperature 25℃Zn C11α5 mol/1
pH4N) (, C11, Omol/1 Cathode current 10A/4W? Anode current 5) -
/dy? Cathode pulse width 3 minutes Anode pulse width 55 minutes Electrolysis time 65 minutes Table 3 Plating solution composition and electrolysis conditions of comparative example 1 Plating solution composition Electrolysis conditions Ni011 1.0mol/l Electrolysis temperature 2
5°C ZnC]4 α3mol/1pH4 NI(4(:!l α5mol/l Cathode current 5)y'tly? Electrolysis time 30 minutes After completion of plating, it was naturally immersed in a caustic soda aqueous solution to dissolve zinc.

FIG. 1 shows the change in electrode potential over time due to the progress of electrolysis in the hydrogen generation reaction of the above electrode. The electrode obtained by the PR plating method of the present invention, Example 1.2, exhibited superior properties in both hydrogen overvoltage and durability compared to Comparative Example 1 in which zinc was dissolved in a conventional caustic solution. Note that Example 1 was created using 30 pulses, and Example 2 was created using 10 pulses.

Example 3 PR plating was carried out in a bath containing cobalt and zinc using the same electrode base material as in Example 1 under the plating solution composition and electrolytic conditions shown in Table 4.

Table 4 Plating solution composition and electrolytic conditions of Example 3 Plating solution composition Electrolytic conditions C! 001. 1.0 mol/1 Electrolysis temperature
25℃ ZnC! 11 α5mol/1p
H4N ) T4 C11, Om Ox7'1 Cand current s A/dm"Anode current
56Vd- Cathode pulse width 60 seconds Anode pulse width 60 seconds Electrolysis time 150 minutes or more The electrode obtained under conditions of 40 A, /eLr
It exhibited a hydrogen overpotential of 160 mV at an electrolytic current of 1. In addition, under the same conditions as Example 1, etc., 2
Although it was used as a hydrogen generating cathode for 1,000 hours, no increase in overvoltage was observed, and it exhibited excellent performance in terms of durability.

[Brief explanation of the drawing]

FIG. 1 shows the change over time in the electrode potential of a Raney alloy activated electrode obtained in one example of the present invention. Figure 2 shows
It is a potential change curve during anode dissolution obtained in a Ni-Zn based bath. Patent applicant Toyo Soda Kogyo Co., Ltd. E/mv, VS R, H, E Time/Sec Anode dissolution potential curve

Claims (1)

[Claims] (1) Forming an alloy film of at least one metal selected from noble metals and at least one metal selected from base metals on a conductive substrate using a cathode current,
A PR plating method characterized by repeating an operation of selectively dissolving and removing base metals in an alloy coating using an anode current.