JP4773168B2 - Electrochemical infrared spectrometer - Google Patents

Description

  The present invention relates to an electrochemical infrared spectrometer capable of measuring an electrode surface in-situ.

  In-situ measurement of electrode surface reaction by infrared spectroscopy enables the elucidation of the electrode reaction mechanism by detecting and identifying the chemical species present on or near the electrode surface. It is expected as a technology that greatly contributes to Specifically, for example, by elucidating the catalytic reaction mechanism in a fuel cell, it is possible to achieve improvement in catalyst utilization, maintenance of catalyst performance over a long period of time, and the like.

  As a method for measuring the electrode surface reaction in situ by infrared spectroscopy, there is a highly sensitive infrared absorption reflection method (IRAS). In the IRAS, infrared light is incident and reflected on the interface between the electrode and the electrolyte, and the intensity of the reflected light is measured to observe the electrode surface (see FIG. 5). In IRAS, infrared light passes through the electrolyte layer before being incident on the interface and after being reflected from the interface (see FIG. 5), but at this time, it is strongly absorbed by the electrolyte. Therefore, in order to suppress absorption of infrared light by the electrolytic solution, the electrolytic solution layer needs to be thinned to about several μm.

However, if the electrolyte layer is made thin, it becomes difficult for the reaction species and reaction products in the electrode reaction to diffuse, and the electrode reaction does not proceed smoothly. In particular, when a gas is generated by an electrode reaction, the generated gas stagnates on the electrode surface, and the spectroscopic measurement is disturbed, making accurate measurement difficult. Furthermore, since the electrolyte layer is thin, it is difficult for current to flow through the electrode, and the electrode reaction is likely to be hindered. In addition, since it is difficult for current to flow through the electrodes, it is difficult to control the electrode potential to a desired value.
Moreover, even if the electrolyte layer is thin, it exists near the electrode surface, and the absorption (background absorption) of the electrolyte layer is significantly larger than the absorption of the chemical species for detection and identification purposes. In addition, it is very difficult to remove background absorption, and information on the electrode surface is difficult to obtain.

  The problem of IRAS as described above can be solved by applying a total reflection (ATR) method using a prism having a metal thin film formed on the bottom surface (see FIG. 1). The ATR method measures the reflection of light (evanescent wave) that leaks slightly from the prism into the electrolytic solution by bringing the prism and the electrolytic solution into close contact with each other. In the ATR method, since infrared light does not pass through the electrolyte layer, the absorption of infrared light by the electrolyte is small and the electrolyte layer can be thickened. Therefore, various problems that occur because the electrolyte layer is thin like IRAS hardly occur in the ATR method.

  Furthermore, at this time, depending on the metal thin film formed on the prism (the type of metal, the particle size of the metal forming the thin film, the film thickness, etc.), the infrared absorption of chemical species present in the vicinity of the metal thin film is significantly increased. The chemical species can be observed with high sensitivity. The infrared absorption enhancement of chemical species by this metal thin film is called surface-enhanced infrared absorption (SEIRA) (see Non-Patent Document 1 and Non-Patent Document 2).

  In the ATR-SEIRAS method in which this SEIRA is combined with the ATR method, the infrared absorption enhancement effect is obtained only in the vicinity of the interface between the metal thin film as an electrode and the electrolytic solution, so that the infrared absorption by the electrolytic solution layer is increased. And only the chemical species present in the vicinity of the electrode surface can be observed with high sensitivity.

M.Osawa “Dynamic Processes in Electrochemical Reactions Studied by Surface-Enhanced Infrared Absorption Spectroscopy (SEARA)” Bull.Chem.Soc.Jpn., 70,2681-2880 (1997) "Infrared Spectroscopy" (Practical Spectroscopy Series), Yukihiro Ozaki, IP Publishing Department, Chapter 4: 6 (pp. 160-170), Masatoshi Osawa

As the prism of the ATR-SEIRA method, silicon (Si) is often used mainly from the viewpoints of infrared transmittance, refractive index, electrochemical stability, and the like. However, since silicon has infrared absorption in a low wavenumber region such as 1000 cm ⁻¹ or less, there is a problem that sensitivity is low with respect to chemical species having infrared absorption in such a low wavenumber region.

The present invention has been accomplished in view of the above circumstances, and the detection and detection of chemical species having infrared absorption in a wave number range where the prism itself has infrared absorption, particularly in a low wave number range of about 1000 cm ⁻¹ or less. It is an object of the present invention to provide an electrochemical infrared spectroscopic device that enables identification.

The electrochemical infrared spectroscopic device of the present invention comprises a total reflection measuring prism and a metal thin film in close contact with the bottom surface of the prism, and an electrolyte is supplied to a surface opposite to the surface in close contact with the prism bottom surface. A working electrode, a counter electrode paired with the working electrode, a reference electrode for regulating the potential of the working electrode, and infrared light from the inside of the prism to the interface between the prism and the working electrode. An electrochemical surface-enhanced infrared absorption spectroscopic device comprising: an optical system for detecting the intensity by introducing infrared light totally reflected at the interface to a detector, wherein the prism includes infrared light in the prism. The metal thin film has a dimension in which metal fine particles having an average particle diameter of 5 to 100 nm are dispersed in an island shape on the metal continuous film, or has a depth from the surface. Has a fine uneven shape of 50 to 100 nm A genus continuous film, and has a thickness of 20 to 100 nm, wherein the optical system, the interface allows condensing the following infrared light spot diameter 2mm infra-red microscope with the working electrode and the prism , it is characterized in that the D ^* has a 10 ⁹ or more infrared sensitive detector.

The present invention suppresses absorption of infrared light by the prism itself by using a prism having such a dimension that the maximum optical path length of infrared light within the prism is 10 mm or less. In this way, by suppressing the interference of the infrared spectroscopic measurement by the prism, it becomes possible to detect and identify the chemical species having infrared absorption in the wave number region where the prism itself has infrared absorption.
In addition, the electrochemical infrared spectroscopic device of the present invention has an infrared microscope and a high sensitivity in order to enable highly sensitive infrared spectroscopic measurement even when a small prism having a maximum optical path length of 10 mm or less is used. A detector is provided.

In order to further suppress infrared absorption by the prism, the prism preferably has a dimension such that the maximum optical path length of infrared light in the prism is 6 mm or less.
Specifically, as a prism having a dimension such that the maximum optical path length of infrared light within the prism is 10 mm or less, the shape is hemispherical or semicylindrical, and the diameter of the semicircular cross section of the prism is 10 mm. The following are mentioned.
The prism is preferably made of silicon (Si) from the viewpoints of infrared light transmittance, refractive index, electrochemical stability, and the like.

In order to stably maintain the conditions of the infrared spectroscopic measurement, it is preferable to keep the concentration of the electrolytic solution supplied to the working electrode constant. As a method for keeping the concentration of the electrolytic solution constant, for example, a method in which the electrolytic solution circulates in a space having the working electrode and the counter electrode as part of an inner wall can be employed.
Examples of the metal thin film include metals exhibiting surface-enhanced infrared absorption, such as Ag, Au, Cu, In, Li, Sn, Pt, Pd, Ni, Al, Pb, Fe, Ir, Rh, Ru, and these metals. And at least one selected from alloys containing at least one of the above.

  According to the present invention, since the interference by the prism is small even in the wave number region where the prism itself exhibits infrared absorption, measurement can be performed with high sensitivity. That is, the infrared spectrum in a wide wave number region can be observed with high sensitivity, and any chemical species can be identified and detected. Therefore, the reaction on the electrode surface can be analyzed in detail by using the electrochemical infrared spectrometer of the present invention.

The electrochemical infrared spectroscopic device of the present invention comprises a total reflection measuring prism and a metal thin film in close contact with the bottom surface of the prism, and an electrolyte is supplied to a surface opposite to the surface in close contact with the prism bottom surface. A working electrode, a counter electrode paired with the working electrode, a reference electrode for regulating the potential of the working electrode, and infrared light from the inside of the prism to the interface between the prism and the working electrode. An electrochemical surface-enhanced infrared absorption spectroscopic device comprising: an optical system for detecting the intensity by introducing infrared light totally reflected at the interface to a detector, wherein the prism includes infrared light in the prism. The maximum optical path length is 10 mm or less, and the optical system has an infrared microscope and an infrared sensitive detector with D ^* of 10 ⁹ or more.

  In the spectroscopic measurement using a prism, when a chemical species to be measured is specified, if a prism having a small absorption in the measurement region of the chemical species is used, the spectroscopic measurement can be performed without being disturbed by the prism. . However, when the chemical species to be measured is not specified, or the target chemical species is specified, it can be used under measurement conditions, and the chemical species is sufficiently absorbed in the measurement region. When there is no optical material for a small prism, it is desirable to reduce the absorption of infrared light by design conditions other than the selection of the optical material, and to suppress the interference of spectroscopic measurement by the prism as much as possible. The interference in measurement by the prism increases as the optical path length of the infrared light in the prism increases.

For example, as described above, silicon (Si) is generally used as a prism for an electrochemical infrared spectrometer from the viewpoints of infrared light transmission, refractive index, electrochemical stability, etc. Since it has infrared absorption in a low wavenumber region such as 1000 cm ⁻¹ or less, the longer the optical path length in the prism, the larger the absorption in the wavenumber region by the prism itself, and the chemical having infrared absorption in the wavenumber region. Species detection / identification becomes difficult.

  Therefore, the present inventors have focused on the fact that the infrared absorption by the prism can be suppressed by shortening the optical path length in the prism as compared with the conventionally used prism, that is, by downsizing the prism. For example, when the prism used in the conventional ATR-SEIRAS method has a semi-cylindrical shape or a hemispherical shape, the diameter (diameter) of the semicircular cross section of the prism is about 20 to 25 mm, that is, the prism. Even if the optical path length of the infrared light inside was short, it was about 20 to 25 mm or more. Conventionally, one of the reasons why such a size prism has been used is that the spot diameter of an infrared beam is 5 to 10 mm in a normal infrared spectrometer, and an infrared beam having such a spot diameter is used. In order to use it efficiently, it is necessary to use a prism having a diameter of about 20 to 25 mm.

  On the other hand, the prism used in the present invention has such a dimension that the maximum optical path length in the prism is 10 mm or less. In this way, by reducing the interference of infrared absorption by the prism as much as possible, it is possible to perform infrared spectroscopic measurement in a wide range of wavenumbers including the wavenumber range in which the prism itself exhibits infrared absorption. Can be detected and identified easily and more accurately.

In the present invention, an infrared microscope is used to efficiently focus infrared light on a miniaturized prism, and further, D ^* is used to detect infrared light focused by the infrared microscope with high sensitivity. by using 10 ⁹ or more sensitivity detector, it realized a sufficiently high sensitivity even using a small prism.

  Hereinafter, the electrochemical infrared spectrometer of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing an example of an electrochemical infrared spectroscopic cell provided in the electrochemical infrared spectroscopic apparatus of the present invention.

  In FIG. 1, a working electrode 2 made of a metal thin film is provided in close contact with a bottom surface (measurement surface) of a total reflection measurement prism (hereinafter sometimes simply referred to as a prism) 1. The working electrode 2 is supplied with the electrolytic solution 3 on the surface opposite to the surface in contact with the prism 1. That is, it is a kretschmann arrangement in which a prism, a metal thin film, and a medium (electrolytic solution) are arranged in the order of prism / metal / electrolytic solution.

  The counter electrode 4 that forms a pair with the working electrode 2 and flows current to the working electrode 2 is also in contact with the electrolytic solution 3, and the electrode reaction proceeds on the contact surface of the working electrode 2 with the electrolytic solution 3. A reference electrode 5 that controls the potential of the working electrode 2 is further in contact with the electrolytic solution 3. In the electrochemical infrared spectroscopic cell shown in FIG. 1, the counter electrode 4 and the reference electrode 5 are arranged in a container 6 filled with the electrolyte solution 3 so that the electrolyte solution 3 is in contact with the counter electrode 4 and the reference electrode 5. Yes.

  The prism 1 is not particularly limited as long as it has a small infrared absorption in the measurement region and has a large refractive index (usually a refractive index of water larger than 1.33), and is generally used in infrared spectroscopy. For example, silicon (Si), germanium (Ge), KRS-5 (thallium bromide iodide), zinc sulfide (ZnS), zinc selenide (ZnSe), sapphire, or the like can be used. Theoretically, the larger the refractive index of the prism, the more the interference caused by infrared absorption of the bulk electrolyte can be further suppressed. Therefore, it is preferable to use a prism having a large refractive index.

Among them, silicon having a large refractive index and excellent in electrochemical stability and chemical stability (acid resistance) is preferable. Silicon is suitable as a prism for the ATR-SEIRA method from the viewpoint of having a wide potential window and excellent adhesion to a metal thin film. However, since silicon exhibits infrared absorption in a low wavenumber region such as 1000 cm ⁻¹ or less, sensitivity in the region is not so good. However, according to the present invention, it is possible to suppress infrared absorption by the prism itself. Therefore, even if a silicon prism is used, infrared that suppresses a decrease in sensitivity in a low frequency region such as 1000 cm ⁻¹ is suppressed. A spectroscopic device can be provided.

In addition, for example, germanium has a high refractive index and has low infrared absorption in a low wavenumber region such as 1000 cm ⁻¹ or less, and can transmit infrared light up to 600 cm ⁻¹ . High sensitivity and excellent optical properties. However, since the chemical stability is low, the working electrode 2 having a desired shape may be formed on the bottom surface of the prism 1 depending on the type of metal constituting the working electrode (metal thin film) 2 and the method for producing the metal thin film. There is a problem that it is difficult. Specifically, when the metal thin film is easily peeled off from the prism, or when a relatively large size crack or pit is generated in the metal thin film, germanium is exposed to the electrolytic solution, and germanium itself is dissolved. is there. Therefore, when germanium is used, it is preferable to appropriately select the metal species constituting the metal thin film described later, the method for producing the metal thin film, the measurement potential region, and the like.

  As described above, the electrochemical infrared spectroscopic device of the present invention has a dimension such that the maximum optical path length of infrared light in the prism is 10 mm or less in order to suppress infrared absorption by the prism itself. It is characterized by Here, the optical path length of the infrared light in the prism is the length of the optical path from when the infrared light is incident from the surface of the prism, totally reflected at the interface between the working electrode and the prism, and emitted from the surface of the prism. is there.

The optical path length of the infrared light in the prism varies depending on the shape of the prism, the infrared light condensing position, the incident angle, and the like. In the present invention, the longest optical path length at a condensing position and an incident angle within a range assumed as a measurement condition of the prism to be used (total critical angle or more because of total reflection measurement) is 10 mm or less. Use a prism. In order to reduce the interference of infrared absorption by the prism, it is preferable to use a prism whose maximum optical path length in the prism is 6 mm or less.
In addition, the smaller the size of the prism is, the more convenient it is for the present invention. However, from the viewpoint of easy production or availability, an O-ring such as silicon rubber or the like between the prism and the cell is used in order to prevent electrolyte leakage. In consideration of sandwiching the sheet, a prism having a maximum optical path length of 3 mm or more is usually used.

  The shape of the prism is not particularly limited, and a general one used in infrared spectroscopy can be used. For example, a hemispherical shape, a semi-cylindrical shape (kamaboko shape), a pyramid shape, a trapezoidal shape and the like can be mentioned. Among these, a hemispherical shape is preferable from the viewpoint that the spot diameter of the infrared light can be narrowed down to a minute region without defocusing.

  In the present invention, when a prism having a spherical shape such as a hemispherical shape or a semi-cylindrical shape is used, in order to set the maximum optical path length to 10 mm or less, the diameter (diameter) of the semicircular cross section of the prism is set to 10 mm or less. do it. Furthermore, in order to make the maximum optical path length 6 mm or less, the diameter of the semicircular cross section of the prism may be about 6 mm or less. The semicircular cross section of the hemispherical or semicylindrical prism referred to here means a semicircle of the prism in a plane passing through the center of the circle that is the bottom surface of the hemispherical prism and perpendicular to the bottom surface. It refers to a semi-circular cross section of a prism in a cross section or a plane perpendicular to the longitudinal direction and the bottom surface of the semi-cylindrical prism.

The working electrode 2 is made of a metal thin film exhibiting surface enhanced infrared absorption (SEIRA), functions as the working electrode 2, and increases the infrared absorption of chemical species existing in the vicinity of the interface between the working electrode 2 and the electrolytic solution. It is something to be made.
The metal thin film showing SEIRA usually has an island-like thin film in which metal fine particles having a diameter of about several tens of nanometers are dispersed in an island shape, or a diameter of about several tens of nanometers on a thin metal continuous film of about 20 to 100 nm. The thing which metal fine particles disperse | distributed to the island form is mentioned. Here, in the metal thin film in which the metal fine particles are dispersed in the form of islands on the metal continuous film, the metal species of the metal continuous film and the metal fine particles present on the metal continuous film may be different or the same. Good.
Alternatively, the metal thin film showing SEIRA may be a thin metal continuous film having fine irregularities with a depth of about 10 to 100 nm on the surface.

  Examples of metals that express SEIRA include Ag, Au, Cu, In, Li, Sn, Pt, Pd, Ni, Al, Pb, Fe, Ir, Rh, Ru, and alloys of these metals (for example, Pt-Fe Alloys) and the like, but are not limited to these, and theoretically, almost all metals are expected to have the same enhancement effect. Among the metals exemplified above, it has been experimentally shown that Ag, Au, Cu, and Pt, in particular, show a high infrared absorption enhancing effect.

  The metal thin film forming the working electrode 2 exhibits SEIRA and has a film thickness that allows evanescent waves to reach the electrolyte and has a film thickness that can ensure electrical conductivity. The film thickness of the metal thin film is not particularly limited. In order to develop sufficient SEIRA strength, in the case of a metal thin film having metal fine particles on the surface, the average particle size of the metal fine particles is preferably about 5 to 100 nm, particularly about 50 to 100 nm. When the average particle size of the metal fine particles exceeds 100 nm, the infrared absorption enhancing effect may be reduced.

Further, in the case of a metal continuous film having a fine uneven shape on the surface, the depth of the fine unevenness from the surface is preferably about 50 to 100 nm in order to develop sufficient SEIRA strength. This is because the SEIRA effect may be lowered on a smooth surface at the atomic level.
Considering that the surface of the metal thin film may be greatly distorted depending on the shape of the surface of the metal thin film on the prism side (the size and shape of the metal fine particles, the size and shape of the irregularities on the continuous film, etc.) It is preferable to design appropriately.

  Further, the thickness of the metal thin film is preferably about 5 to 100 nm, and particularly about 20 to 100 nm in order to ensure sufficient electric conductivity. When the film thickness of the metal thin film exceeds 100 nm, the dispersibility of the metal fine particles is lowered, the metal fine particles are fused, and it is difficult to form a metal thin film in which the metal fine particles are dispersed in an island shape. As a result, the SEIRA intensity may decrease. However, even in a metal thin film in which metal fine particles are fused with each other, there are many irregularities such as pits and cracks on the surface of the metal thin film, and the infrared absorption may be enhanced by the irregularities of these metal thin films. Therefore, it is not always necessary for the metal thin film to have metal fine particles dispersed on the surface, or to have fine irregularities as described above on the surface, but the infrared absorption enhancing effect is high. Therefore, a metal thin film having metal fine particles dispersed in islands or a metal thin film having fine irregularities as described above is preferable to a metal thin film having relatively large irregularities such as cracks and pits.

  The film thickness of the metal thin film is the thickness of the entire metal thin film, and those having metal fine particles on a continuous film or those having fine irregularities have a thickness including these metal fine particles and fine irregularities. The thickness of the metal thin film.

  In order to ensure sufficient electrical conductivity as a working electrode and a high SEIRA effect at the same time, metal fine particles are densely dispersed in an island shape on the metal continuous film, or fine irregularities are formed on the metal continuous film. A metal thin film is preferable.

  The metal thin film showing SEIRA as described above is thin enough to allow the evanescent wave to penetrate to the surface (electrode surface) opposite to the surface in contact with the prism, and is irradiated with infrared light from the back side of the electrode. It is possible to observe the electrode surface.

  Here, the average particle diameter of the metal fine particles is an average value of the long and short diameters of the metal fine particles, and includes a scanning electron microscope (SEM), a scanning tunneling microscope (STM), a scanning atomic force microscope (AFM), and the like. Can be measured by observation. Moreover, the film thickness of a metal thin film can be converted from the weight measurement by a quartz crystal microbalance, or can be measured by SEM, STM, AFM, etc.

The method for producing the metal thin film as described above is not particularly limited, and examples thereof include vacuum deposition, electrolytic plating, electroless plating, and sputtering. The vacuum deposition method is easy to produce a metal thin film that expresses SEIRA, and has a wide selection of metal species. Electroless plating can form a metal thin film that ensures sufficient electrical conductivity and SEIRA effect at the same time. In addition, electroless plating is the simplest method and can form a metal thin film having excellent adhesion to the prism. Examples of established conditions for forming a metal thin film by electroless plating include Ag, Au, Cu, Pt, and Pd.
Since the SEIRA effect is greatly influenced by conditions (for example, the deposition rate in the vacuum deposition method, the composition of the plating solution and the plating temperature in the electroless plating method) at the time of forming the metal thin film, it is preferable to appropriately set the conditions.

In addition, if the adhesion between the metal thin film and the prism is poor, problems such as peeling of the metal thin film from the prism during measurement occur, so the adhesion between the metal thin film and the prism is important. In order to improve the adhesion between the prism and the metal thin film, for example, surface treatment may be performed on the bottom surface of the prism before the metal thin film is formed. Measurement sensitivity can be increased by improving the adhesion between the prism and the metal thin film. For example, as a surface treatment when a silicon prism is used, a mercaptosilane treatment or the like can be given.
The electrode surface is preferably cleaned by repeating oxidation-reduction (oxide formation region-hydrogen generation region) by electric potential in the electrolytic solution. This is because contamination of the electrode surface significantly hinders the observation of the electrode reaction.
Regarding SEIRA, Non-Patent Document 1, Non-Patent Document 2, and the like described above can be referred to.

  Infrared light collected from the inside of the prism 1 to the interface between the prism 1 and the working electrode 2 enters the interface at an incident angle larger than the critical angle and is totally reflected. At this time, the evanescent wave penetrates to the opposite surface (electrode surface) of the metal thin film which is the working electrode 2 and is absorbed by chemical species existing in the vicinity of the interface between the working electrode 2 and the electrolytic solution 3 at the time of reflection. Therefore, by detecting the intensity of the reflected light emitted from the interface between the prism 1 and the working electrode 2 and analyzing the absorption spectrum, detection and identification of the chemical species existing in the vicinity of the interface between the working electrode 2 and the electrolytic solution 3 are performed. Can do. At this time, the infrared absorption of the chemical species is remarkably increased by the effect of enhancing the infrared absorption of the metal thin film that is the working electrode 2, so that detection and identification can be performed with high sensitivity.

  Here, the chemical species present near the interface between the working electrode 2 and the electrolytic solution 3 are not only the adsorbing species adsorbed on the surface of the working electrode, but also the working electrode without adsorbing on the surface of the working electrode 2. Those floating in the vicinity of the interface between 2 and the electrode liquid 3 are also included, and examples include reaction products, reaction intermediates, and reaction byproducts in electrode reactions.

The electrochemical infrared spectroscopic apparatus of the present invention utilizes the effect of increasing infrared absorption by SEIRA, and enables highly sensitive in-situ measurement of the electrode surface. Also, by using the ATR arrangement, unlike IRAS, infrared light is incident from the prism side to the interface between the prism and the working electrode, so the absorption of infrared light by the electrolyte is small and it exists near the electrode surface. There is almost no interference with the measurement of chemical species.
In addition, for the IRAS where the electrolyte layer needs to be thinned to about 1 to 2 μm, the infrared spectroscopic device of the present invention using the ATR arrangement has no limitation on the thickness of the electrolyte layer. The diffusion of components is not hindered and the electrode reaction proceeds smoothly. In particular, even when a gas is generated by an electrode reaction, compared to IRAS, the generated gas is less likely to stay on the electrode surface, so that there is less interference with infrared spectroscopic measurement due to the generated gas. Furthermore, unlike IRAS, problems such as interference of electrode reaction due to difficulty in current flow and difficulty in controlling electrode potential do not occur.

The electrolytic solution 3 serves as a medium for passing a current between the working electrode 2 and the counter electrode 4, and contains a reactive species that undergoes an oxidation or reduction reaction at the working electrode 2. Examples of the electrolytic solution include an oxidation reaction species or a reduction reaction species, an electrolyte solution in which an electrolyte that generates an oxidation reaction species or a reduction reaction species is dissolved, and a component that conducts ion conduction with an oxidation reaction species or a reduction reaction species. And the like. Here, the oxidation reaction species or the reduction reaction species include a precursor that generates an oxidation reaction species or a reduction reaction species in the electrolyte under measurement conditions. Specifically, an acidic aqueous solution in which oxygen gas and hydrogen gas are dissolved, a mixed solution of methanol and an acidic solution, or the like can be given.
Except for the purpose of measuring the reduction reaction of oxygen, etc., the electrolytic solution uses Ar gas, N ₂ gas, or the like in order to ensure reproducibility and avoid complicated reactions. It is necessary to exclude.

  The material and shape of the counter electrode 4 are not particularly limited as long as a current can be passed through the working electrode 2 to be observed. Moreover, the reference electrode 5 should just show the stable electric potential used as the reference | standard of the electric potential of a working electrode in the electrolyte solution to be used, a standard hydrogen electrode (SHE or NHE), a saturated calomel electrode (SCE), a reversible. A hydrogen electrode (RHE), a silver-silver chloride electrode (Ag / AgCl), or the like can be used.

The concentration of the electrolytic solution 3 supplied to the working electrode 2 is preferably kept constant as an observation condition of the electrode surface. From such a viewpoint, the electrolytic solution 3 is preferably supplied by a flow system as shown in FIG.
In FIG. 2, the electrolyte 3 flows through a conduit 8 communicating with the container 7 containing the electrolytic solution 3, and the electrolytic solution 3 is not retained on the surface of the working electrode 2. Further, in FIG. 2, the counter electrode 4 together with the working electrode 2 constitutes the inner wall of the conduit 8 and is opposed to each other. At this time, the reference electrode 5 can be disposed in the container 7.

As a means for supplying the electrolytic solution to the working electrode in this way, by adopting a flow system for circulating the electrolytic solution in the space (conduit 8) having the working electrode and the counter electrode as part of the inner wall, Besides improving the diffusibility, the electrochemical infrared spectroscopic cell can be made compact, and the compact design of the electrochemical infrared spectroscopic cell accompanying the miniaturization of the prism becomes easy. In addition, when the cell is downsized by adopting the flow system, it is difficult to perform the process of removing oxygen from the electrolyte solution using Ar gas, N ₂ gas, or the like in the cell. It will flow.

Since the electrochemical infrared spectroscopic cell can be downsized and the electrolyte flow rate can be increased, the height of the electrolyte layer in the flow system (the height of the conduit, the working electrode-the distance of the wall facing the working electrode) Is preferably about 0.1 to 5 mm. Increasing the flow rate of the electrolyte has the advantage that the influence of substance diffusion can be reduced.
In addition, by adopting a flow system, the reaction product can be led to high performance liquid chromatography (HLPC) or a mass analyzer for analysis.

  When using a small prism as in the present invention, unless infrared light is focused to a spot diameter that matches the size of the prism bottom surface, light loss occurs and it is difficult to perform infrared spectroscopic measurement. Therefore, it is necessary to narrow down infrared light using an infrared microscope. The narrowing of the spot diameter of the infrared light may be appropriately adjusted according to the shape and size of the prism used and the size of the electrode region to be observed. However, the size of the prism provided in the infrared spectroscopic device of the present invention is usually 2 mm. It is necessary to narrow down to the following. If an infrared microscope is used, the spot diameter of infrared light can be narrowed down to about 10 to 20 μm in principle. What is necessary is just to use the general thing used for an infrared microspectroscope as an infrared microscope.

As described above, when infrared light is condensed on the bottom surface of a small prism, that is, in a minute region by using an infrared microscope, D ^* 10 ⁹ or more capable of detecting weak light for detecting reflected light. It is necessary to use a highly sensitive detector. D ^* is a parameter representing the sensitivity of the detector, and the larger the value, the higher the sensitivity of the detector. As a standard, a pyroelectric detector DTGS or a semiconductor detector with higher sensitivity than TGS, which is installed as standard in the FT-IR spectrometer, can be used. The high-sensitivity detector is usually used while being cooled with liquid nitrogen or helium.
D ^* is The 10 ⁹ or more sensitivity detector, which is generally used, for example, 800～4000Cm liquid nitrogen-cooled high in the wave number region of ^-1 sensitivity MCT detector, 2000 cm ^-1 or more wavenumber region In measurement, an InSb detector can be used, and a bolometer, etc. can be used in measurement in the wavenumber region below 1000 cm ⁻¹ .

  In the present invention, the infrared light is condensed from the inside of the prism to the interface between the prism and the working electrode, and the infrared light totally reflected at the interface is guided to the detector. In addition to the infrared microscope and high-sensitivity detector, the optical system for detecting the intensity includes a light source for infrared light, a lens and a reflecting mirror for generating and extracting parallel light and convergent light from the emitted light, a slit, etc. Other members are included in appropriate combinations. It is expected that a higher S / N ratio can be obtained by using a synchrotron high-intensity light source as the light source.

  FIG. 4 shows a form example (FT-IR spectrometer) of the electrochemical infrared spectrometer of the present invention. In FIG. 4 (4A), the infrared light irradiated from the light source is guided to the interface between the working electrode and the prism in the sample chamber by a beam splitter or a reflecting mirror, and the reflected light reflected at the interface is sent to the detector. It is guided. To the infrared microscope, a plane mirror is used to guide infrared light from the spectroscope to the infrared microscope (see FIG. 4 (4B)). In the case of image measurement, infrared light is guided to an external optical system (not shown) for image measurement using a plane mirror.

The in-situ measurement of the electrode surface by the electrochemical infrared spectrometer of the present invention can be performed in accordance with a general method.
If necessary, control the potential of the working electrode using a potentiostat for potential control, keep the potential constant, or measure the infrared absorption spectrum while measuring the current by scanning the potential. Also good. In addition, an electrochemical infrared spectrometer using SEIRA as in the present invention is effective for time-resolved measurement for measuring an infrared absorption spectrum that changes in the order of microseconds to milliseconds. This is because time-resolved measurement requires a sufficiently large signal, but an electrochemical infrared spectrometer using SEIRA can increase the signal. Time-resolved measurement enables detection and identification of reaction intermediates with a short lifetime.

  The electrochemical infrared spectroscopic apparatus of the present invention enables detailed elucidation of the electrode reaction mechanism on the electrode surface, for example, the catalyst surface of a fuel cell. Furthermore, it can also be suitably used for observation of plating processes, metal corrosion, various surface treatments, and the like.

(Reference experiment example)
Single beam spectra of a hemispherical Si prism having a semicircular cross-section radius of 10 mm (ie, optical path length of 20 mm) and a hemispherical Si prism having a semicircular cross-section radius of 5 mm (ie, optical path length of 10 mm) were measured. The results are shown in FIG.

In a prism with a radius of 10 mm and an optical path length of 20 mm, the signal intensity became zero in the wave number region of 1000 cm ⁻¹ or less, and a spectrum was not obtained.
On the other hand, with a 5 mm radius prism with an optical path length of 10 mm, infrared light was transmitted up to 630 cm ⁻¹ and a spectrum could be obtained. Therefore, if the prism is made smaller and the spot diameter of the infrared light is narrowed down with an infrared microscope, the signal intensity is further increased, and the resulting signal-to-noise ratio of the spectrum is increased, resulting in highly accurate infrared light. It can be seen that spectroscopic measurement is possible.

It is a schematic diagram which shows one form of the electrochemical infrared spectroscopy cell with which the electrochemical infrared spectroscopy apparatus of this invention is equipped. It is a schematic diagram which shows one form of the electrochemical infrared spectroscopy cell with which the electrochemical infrared spectroscopy apparatus of this invention is equipped. It is a single beam spectrum of a prism having a radius of 5 mm (optical path length in the prism of 10 mm) and a prism having a radius of 10 mm (optical path length in the prism of 20 mm). It is the schematic which shows the example of 1 form of the electrochemical infrared spectroscopy apparatus of this invention. It is a schematic diagram which shows one form of the electrochemical infrared spectroscopy cell used for the conventional electrochemical infrared spectroscopy (IRAS) method.

Explanation of symbols

1 ... Total reflection measuring prism 2 ... Working electrode (metal thin film)
3 ... Electrolyte 4 ... Counter electrode 5 ... Reference electrode 6 ... Vessel 7 ... Vessel 8 ... Conduit

Claims (6)

A total reflection measuring prism, a working electrode made of a metal thin film in close contact with the bottom surface of the prism, and an electrolyte supplied to a surface opposite to the surface in close contact with the prism bottom surface; A counter electrode that defines the potential of the working electrode, a reference electrode for regulating the potential of the working electrode, and infrared light that is condensed from the inside of the prism to the interface between the prism and the working electrode, and the infrared light that is totally reflected at the interface. An electrochemical surface-enhanced infrared absorption spectroscopic device comprising: an optical system that detects the intensity by leading to a detector;
The prism has a dimension such that the maximum optical path length of infrared light in the prism is 10 mm or less,
The metal thin film is a metal continuous film in which metal fine particles having an average particle diameter of 5 to 100 nm are dispersed in an island shape on a metal continuous film or a fine continuous film having a depth from the surface of 50 to 100 nm. And having a thickness of 20 to 100 nm,
Wherein the optical system, an infrared microscope capable condensing the following infrared light spot diameter 2mm at the interface between the working electrode and the prism, the D ^* has a 10 ⁹ or more infrared sensitive detector An electrochemical infrared spectrometer characterized by   The electrochemical infrared spectroscopic apparatus according to claim 1, wherein the prism has a dimension in which a maximum optical path length of infrared light in the prism is 6 mm or less.   The electrochemical infrared spectroscopic apparatus according to claim 1 or 2, wherein the prism has a hemispherical shape or a semi-cylindrical shape, and a semicircular cross section of the prism has a diameter of 10 mm or less.   The electrochemical infrared spectrometer according to any one of claims 1 to 3, wherein the prism is made of silicon (Si).   5. The electrochemical infrared spectrometer according to claim 1, wherein the electrolytic solution circulates in a space having the working electrode and the counter electrode as part of an inner wall. The metal thin film is at least one selected from Ag, Au, Cu, In, Li, Sn, Pt, Pd, Ni, Al, Pb, Fe, Ir, Rh, Ru, and an alloy containing at least one of these metals. The electrochemical infrared spectrometer according to any one of claims 1 to 5, wherein the electrochemical infrared spectrometer is formed of seeds.

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