JP3310995B2 - Bipolar cell for voltammogram recording and voltammogram recording method using this bipolar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltammogram recording cell and a voltammogram recording method. Here, the voltammogram refers to a record of electrochemical measurement of oxidation / reduction characteristics of a compound. The record takes the form of an applied current curve or a spectral change, and analysis of this record allows determination of properties such as redox potential, reaction rate, and reactivity.

[0002]

2. Description of the Related Art In a conventional voltammogram recording method, a working electrode, a counter electrode and a reference electrode are used as electrodes, the potential of the working electrode is changed with reference to the potential of the reference electrode, and the current value at that time is recorded to apply an applied voltage. The curve is recorded.

[0003]

In the conventional voltammogram recording method, a triode type cell is used, so that the configuration of the cell is complicated. In particular, various films such as an electrochromic element, an electroluminescent element, and a photoelectric response element are used. It was very difficult to measure the electrochemical properties of the used electrochemical device using a three-electrode cell.

An object of the present invention is to simplify the structure of a voltammogram recording cell and to easily measure the electrochemical characteristics of an all-solid-state device.

[0005]

The voltammogram recording cell of the present invention that achieves the above object has two different redox reaction electrodes arranged face-to-face, and the redox reaction systems of these electrodes are not mixed. It is composed. The redox reaction electrode may be formed by bringing the redox reaction system into contact with the conductive electrode substrate in the form of a film or a solution. In this case, if the electrode substrate is a light-transmitting, particularly transparent conductive glass, it is convenient for recording in the form of a spectrum change. Further, the redox reaction electrode can be formed of a conductive film containing a redox reaction system without using an electrode substrate.

[0006] In the voltammogram recording method of the present invention which achieves the above object, two electrode substrates face each other, a first redox reaction system is brought into contact with one electrode in the form of a film or a solution, and the other electrode is brought into contact with the other electrode. The second redox reaction system is brought into contact with the first redox reaction system in the form of a film or a solution so as not to be mixed with the first redox reaction system, and a potential is applied to both electrodes, and the potential difference is changed to record a current value. . In this case, the potential difference is changed in one direction (the direction in which the reaction occurs) and then in the other direction at least once so that processing such as averaging can be performed to reduce the influence of the measurement error due to the reaction speed and the history phenomenon. Is also good. In order to determine the redox potential of a given redox compound among the electrochemical properties, a redox reaction system having a known redox potential and a redox reaction system having an unknown redox potential are used to oxidize both redox systems. The unknown redox potential can be determined as the difference between the potential difference when the reduction reaction occurs and the known redox potential.

Instead of applying a potential to both electrodes and changing the potential difference to record a current value, instead of applying a potential to both electrodes and changing the potential difference to record a change in a redox absorption spectrum. Good. Of particular note is the application of a potential to both electrodes, changing the potential difference to record the current value, and at the same time, recording the change in the absorption spectrum of the redox system, thereby increasing the reliability of the recording by intercomparison. The amount of information on electrochemical properties can be increased.

The electrode material may be a conventional triode cell electrode material, for example, platinum, carbon or other metal, or transparent conductive glass. When a plate or a film-like electrode is used, it is preferable to arrange the electrodes so that the surface in which the reaction takes place is faced inside.

[0009]

FIG. 1 shows an embodiment of a bipolar cell for voltammogram recording according to the present invention. This example is a liquid (I) / partition / liquid (II) type cell (here, (I) and (II) indicate different redox systems). The redox reaction systems 3, 4 are in contact with the respective electrodes 1, 2 in the form of a solution, and the septum 5 prevents the two redox reaction systems from mixing. 6 is a spacer, 7,
8 is a lead wire. The electrodes 1 and 2 may be made of a translucent material, for example, transparent conductive glass, so that an absorption spectrum accompanying the reaction can be recorded.

As another embodiment, a membrane (I) / liquid (II) type cell, a membrane (I) / partition / liquid (II) type cell, a membrane (I)
/ Cells / membrane (II) type cells, membrane (I) / liquid / membrane (II) type cells, membrane (I) / membrane (II) type cells, and the like. The solution may be any liquid that dissolves or suspends the redox system and the electrolyte. Water is most often used, but also acetonitrile, dimethylformamide (DMF),
Polar organic solvents such as tetrahydrofuran and dioxane can also be used. An electrolyte is preferably dissolved in these solutions in order to improve the conductivity.

As the film, any material can be used as long as it is a material capable of retaining a redox system and is not dissolved in the medium to be used and is electrochemically inert. For example, when the redox system is a cation, a polyanion membrane is used, and when the redox system is an anion, a polycation membrane is used, whereby the redox system can be held electrostatically well. Examples of the polyanion film include naphthion, sodium polystyrene sulfonate, acrylate of a homopolymer or copolymer of acrylic acid and a derivative thereof, and the like. Examples of the polycation membrane include pyridinium salts of vinyl pyridine and vinyl bipyridine homopolymers and copolymers, a polymer having a quaternary ammonium base, and a polymer having a cationic metal complex group. In addition, solid electrolyte membranes, or clay or zeolites,
Inorganic compounds such as silica gel and alumina can also be used as a coating film that holds redox species.

In order to disperse the redox species in these films, a film is formed on the electrode surface in advance by a casting method, an immersion method, a spin coating method or the like, and then the redox species is adsorbed from a solution, or the redox species is previously dispersed with the film components. After adjusting the mixed solution of the redox species, the film can be formed on the surface of the electrode substrate by the above-described method. Alternatively, a redox species which is previously reacted with a compound constituting a membrane and introduced by a covalent bond is synthesized, and when this is formed into a membrane, it is used as a stable redox system without fear of elution.

Materials used in ordinary electrochemistry, such as glass filters, ceramics, ion exchange membranes, solid electrolyte membranes, and other polymer membranes may be used as the partition walls in which different redox systems are not mixed. The thickness of the solution layer or the film may be arbitrary, but the reaction occurs near the electrode, so that it can be measured even if it is thin. For example, a solution layer or film having a thickness of 0.01 μm to 10 mm is used.

The shape of the effective reaction surface of the electrode is usually selected from a rectangle, a square and a circle. The electrode area can correspond to any size from a micro type to a large type. Usually, the area is 1 square millimeter to 10 square centimeters. FIG. 2 shows an embodiment of a micro-type cell. Different redox reaction systems 3 and 4 are brought into contact with the tips of lead wires 7 and 8 of platinum or carbon having a flattened tip of 1 micron diameter in the form of a solution or a membrane, and a separation membrane ( (Or solution) 5.

FIG. 3 shows an embodiment of a micro-type cell which is convenient for detecting and recording a redox reaction by a change in absorption spectrum. In FIG. 3, the same elements as those in FIG. 2 are indicated by the same numbers. An optical fiber 10 is provided with a conductive film 9 such as tin oxide or indium oxide, and has lead wires 7 and 8 attached thereto. To measure the ultraviolet / visible absorption spectrum, the cell is also irradiated with measurement light from one side using the optical fiber 10 and the transmitted light is measured from the opposite side.

As the see-through type electrode, a transparent conductive glass in which glass is coated with tin oxide or indium oxide is most easily used. In addition, a glass electrode on which a thin film of translucent gold or aluminum is vapor-deposited, or a metal such as gold is coated on the glass surface. Alternatively, a glass electrode or the like deposited in a comb shape can be used. With such optical information collecting means, not only the ingress and egress of charges but also the change of chemical species can be directly observed in the spectrum.

In practicing the present invention for determining the redox potential, a redox system having a known redox potential is used for one of the electrodes. If an unknown electrode is used, the redox potential is determined in advance by a normal triode voltammograph. You only have to decide. The redox species may be a metal, a metal ion, a metal complex, an organic redox system, or the like. In the case of metal, this can be used directly as an electrode. When water is used as a medium, oxidation of water or reduction of protons can be used as a counter electrode redox system. Since an electric current is generated only when a reaction in the opposite direction occurs on both electrodes, an oxidant is used on the other electrode if a reductant is used on one electrode.

Hereinafter, an example of a bipolar cell for recording a voltammogram of the present invention and a method for recording a voltammogram using the bipolar cell will be described. Example 1 : 8 μl of an alcohol solution (2.5% by weight) of naphion (made by DuPont) was dropped and spread on an electrode substrate having an effective area of 1 square cm and coated with indium tin oxide on glass, air-dried at room temperature, and distilled water. For 30 minutes and then air dried at room temperature. This was immersed in a 1 mM aqueous solution of methyl viologen (MV ²⁺ ) for 1 hour to adsorb MV ²⁺ ,
Washed with water. A 1 mM aqueous solution of tris (2,2′bipyridine) ruthenium (II) complex (Ru (bpy) ₃ ²⁺ ) was used to prepare Ru (b)
py) ₃ ²⁺ was adsorbed, it was washed with water. These electrodes are separated by spacers made of a plastic film having a thickness of 250 microns, and an aqueous electrolyte solution (0.1 M HCl-KC) is used.
1, pH 2) was added to make a bipolar cell.

Example 2 : Ru using the bipolar cell of Example 1
(Bpy) ₃ polarity of ²⁺ side is 0V → + 2V → 0V → -2V
The potential difference between the two electrodes was swept at a rate of 20 mV / sec so as to become 0 V, and the current value was recorded to obtain a bipolar cyclic voltammogram shown in FIG. Potential difference at the midpoint of the positive and negative sides of the current peak 1.73V is Ru (bpy) ₃ ²⁺ and MV
²⁺ redox potential difference (1.07 − (− 0.69) =
1.76V). In the part of the positive current, Ru at the working electrode
^{_{(Bpy) 3 2+ → Ru (}} bpy) 3 3 + oxidation has occurred, and has arisen MV ²⁺ → MV ^+. The reduction in the counter electrode at the same time. In the case of the negative current, the opposite reaction occurs. If one redox potential is known, the other unknown redox potential is determined from the cyclic voltammogram.

Example 3 : Light from a xenon lamp is radiated from one side of the bipolar cell of Example 1 using a quartz optical fiber, and light transmitted to the other side is received by the quartz optical fiber and is converted by a monochromator. After the spectroscopy, the transmitted light intensity was measured by a diode array detector, and the relationship between the wavelength and the absorbance was recorded as an absorption spectrum to obtain the graph of FIG. Before the voltage sweep based on the Ru (bpy) ₃ ²⁺ 45
0 nanometer of absorption can be seen but, Ru (bpy) ₃ ²⁺
The positive side, the MV ²⁺ absorption in to the 450 nanometer swept in the negative side decreases, resulting from MV ²⁺ instead M
The absorption at 500-600 nanometers based on V ⁺ is increased. As the potential difference is reduced from 2 V, the spectrum reversibly returns. From this, it can be seen that a redox reaction as described in Example 2 occurs in both poles.

Practical Example 4 : An electrode in which Ru (bpy) ₃ ²⁺ is adsorbed on a indium tin oxide with a naf ion film adsorbed thereon is used as a working electrode, and an electrode in which only a naf ion film is coated on indium tin oxide is used as a counter electrode. A 1 M HCl-KCl buffer aqueous solution (pH 2) was placed between both electrodes to form a cell. No partitions are used. When the potential difference between both electrodes was swept, the redox potential of Ru (bpy) ₃ ^{2 + / 3 +} (1.
31 V) and the redox potential of proton reduction (−0.12
V) (red 1.49 V), a redox waveform was observed reversibly across the potential difference, and the Redox reaction of Ru (bpy) ₃ ²⁺ ⇔Ru (bpy) ₃ ³⁺ It was confirmed that it had occurred. Thus, even when proton reduction occurs on the counter electrode side, a cyclic voltammogram can be obtained (see FIG. 6).

Example 5 : Ru (b) was added to the naphion film of Example 4.
MV ²⁺ Nafuion film py) ₃ ²⁺ instead of adsorbing
A similar cell was made using an electrode on which was adsorbed. From the cyclic voltammogram recorded using this cell, a redox reaction corresponding to MV ^{2 + / +.} Redox reaction and water oxidation was observed. Thus, a cyclic voltammogram can be obtained even if the oxidation of water is used on the counter electrode side.

Example 6 : In Example 1, both electrodes were separated by a plastic film spacer and an aqueous electrolyte solution (0.1 M
HCl-KCl, pH 2) was added, but instead of this electrolyte aqueous solution, a 180 micron thick naph ion membrane impregnated with a 0.1 M KCl aqueous solution was used to make a bipolar cell. Spectrocyclic voltammograms were recorded as in Examples 2 and 3 (see FIG. 7).

[0024]

According to the present invention, a voltammogram accompanying a redox reaction can be recorded in the form of an applied voltage / current curve or a spectrum change in a cell having a simple structure. In particular, when recording in both formats simultaneously, changes in chemical species can be directly and visually observed. Since the configuration of the present invention is suitable for microfabrication and can be measured in the same environment as an electrochemical device using a film or the like, it is suitable for examining electrochemical characteristics of an electrochromic device, an electroluminescent device, a photoelectric response device, and the like. Particularly useful.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a bipolar cell of the present invention.

FIG. 2 is a schematic diagram showing one embodiment of a bipolar cell of the present invention.

FIG. 3 is a schematic diagram showing another embodiment of the bipolar cell of the present invention.

FIG. 4 shows an example of a cyclic voltammogram recorded using the bipolar cell of the present invention.

FIG. 5 shows an example of an absorption spectrum associated with a redox reaction recorded using the bipolar cell of the present invention.

FIG. 6 shows an example of a cyclic voltammogram recorded using the bipolar cell of the present invention.

FIG. 7 shows another example of a cyclic voltammogram recorded using the bipolar cell of the present invention.

[Explanation of symbols]

 Reference Signs List 1 electrode 2 electrode 3 redox reaction system 4 redox reaction system 5 partition wall 6 spacer 7 lead wire 8 lead wire 9 conductive film 10 optical fiber

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor, Nyoaki Hayashi 29-1, Honchoso, Wako-shi, Saitama 102-1, Honbashi-so 102 (56) References JP-A-2-197590 (JP, A) JP-A-55-87942 ( JP, A) JP-A-2-254352 (JP, A) JP-A-60-168045 (JP, A)

Claims (11)

(57) [Claims] 1. A redox reaction electrode in contact with a first redox reaction system is arranged facing a redox reaction electrode in contact with a second redox reaction system, and the redox reaction systems of these electrodes are not mixed. A bipolar cell for voltammogram recording, characterized in that it is constituted. 2. The bipolar cell for voltammogram recording according to claim 1, wherein the redox reaction electrode is formed by bringing the redox reaction system into contact with the conductive electrode substrate in the form of a film or a solution. 3. The bipolar cell for recording a voltammogram according to claim 2, wherein the electrode substrate is translucent. 4. The bipolar cell for voltammogram recording according to claim 3, wherein the electrode substrate is a transparent conductive glass. 5. The bipolar cell for voltammogram recording according to claim 1, wherein the redox reaction electrode is a conductive film or a metal containing a redox reaction system. 6. A method in which two conductive electrode substrates face each other, one electrode is brought into contact with a first redox reaction system in the form of a film or a solution, and the other electrode is mixed with the first redox reaction system. A voltammogram recording method characterized by contacting the second redox reaction system in the form of a film or a solution without applying a voltage, applying a potential to both electrode substrates, and changing the potential difference to record a current value. 7. The voltammogram recording method according to claim 6, wherein the change in the potential difference is performed at least once in one direction and then in the other direction. 8. The redox potential of the first redox reaction system is known, the redox potential of the second redox reaction system is unknown, and the potential difference when the oxidation and reduction reactions of both redox systems occur is known. The voltammogram recording method according to claim 6 or 7, wherein an unknown redox potential is determined as a difference from the redox potential of (1). 9. A method in which two conductive electrode substrates face each other, one electrode is brought into contact with a first redox reaction system in the form of a film or a solution, and the other electrode is mixed with the first redox reaction system. A voltammogram characterized by contacting the second redox reaction system in the form of a membrane or a solution without applying the same, applying a potential to both electrodes, and changing the potential difference to record a change in the absorption spectrum of the redox system. Recording method. 10. The voltammogram recording method according to claim 9, wherein the change in the potential difference is performed at least once in one direction and then in the other direction. 11. The redox potential of a first redox reaction system is known, the redox potential of a second redox reaction system is unknown, and the potential difference when an oxidation / reduction reaction of both redox systems occurs is known. The voltammogram recording method according to claim 9, wherein an unknown redox potential is determined as a difference from the redox potential of the voltammogram.