JP2007078488A - Electrochemical infrared spectroscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical infrared spectroscope capable of objectively measuring a plurality of samples efficiently under the same condition at the same time. <P>SOLUTION: An electrochemical surface increasing infrared absorbing spectroscope is equipped with a total reflection measuring prism, an acting electrode comprising a metal thin film closely bonded to the base of the prism and supplied with an electrolyte on the opposite face of a face, the counter electrode forming a pair along with the acting electrode, a reference electrode for prescribing the potential of the acting electrode and an optical system for condensing infrared rays to the interface of the prism and the acting electrode from the interior of the prism and guiding the infrared rays totally reflected from the interface to a detector to detect the intensity thereof. A plurality of the acting electrodes are provided per the prism. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrochemical infrared spectrometer, and more particularly to an electrochemical infrared spectrometer capable of in-situ measurement of a plurality of electrode surfaces.

  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. 9). In the IRAS, infrared light passes through the electrolyte layer before being incident on the interface and after reflection from the interface (see FIG. 9), 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. 10). 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.

  On the other hand, in the infrared spectroscopic measurement, not only one infrared spectrum is obtained at one measurement point, but also the number of measurement points is increased and mapping analysis is performed by measuring the infrared spectrum at a plurality of points on the sample surface. Yes. Examples of such infrared spectrum measurement techniques at a plurality of points include those described in Patent Document 1 and Patent Document 2.

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 JP-A-11-190694 JP 2002-214131 A

Conventionally, in the ATR-SEIRAS method, when a thin film of a metal having different surface structure, metal composition, etc. is used as an electrode and systematic observation of the electrode surface is performed, the infrared absorption spectrum is measured for each electrode made of each metal thin film. Was done. That is, it is necessary to exchange prisms or electrochemical infrared spectroscopic cells for each measurement, which is very troublesome. In addition, due to fluctuations in the metal composition of the metal thin film that is an electrode and dissolution of metal species from the metal thin film into the electrolyte, it was not easy to keep the measurement conditions constant, and reproducibility was low.
As described above, in the conventional ATR-SEIRAS method, it is difficult to measure a plurality of samples efficiently and objectively under the same conditions. In particular, when observing the surface of an electrode made of an alloy electrode catalyst, it is difficult to compare the activity of the alloy catalyst because dissolution of metal species occurs during setup.

  The present invention has been accomplished in view of the above circumstances, and an object thereof is to provide an electrochemical infrared spectrometer capable of measuring a plurality of samples efficiently and simultaneously under the same conditions. is there.

  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 apparatus comprising: an optical system for detecting the intensity by introducing infrared light totally reflected at the interface to a detector, and A plurality of electrodes are provided.

  Since the electrochemical infrared spectroscopic device of the present invention is provided with a plurality of working electrodes for one prism, it is possible to observe a plurality of electrode surfaces simultaneously. Further, by providing a plurality of working electrodes for one prism, the measurement conditions between a plurality of samples can be made the same.

  When at least one of the plurality of working electrodes is made of a metal thin film having a metal composition different from that of at least one other working electrode, research on alloy electrode catalysts, for example, systematic activity of alloy electrode catalysts Comparison and the like are possible.

  Since it is possible to perform systematic observation of the electrode surface by controlling measurement conditions, grasping the state of the electrode, and the like, it is preferable that the electrode potential of each of the plurality of working electrodes can be controlled independently. Further, from the same viewpoint as described above, it is preferable that each of the plurality of working electrodes can independently detect a current flowing through the working electrode.

The method of irradiating the plurality of working electrodes with infrared light is not particularly limited. However, from the viewpoint of efficiently performing spectrum measurement of each electrode by arranging a large number of electrodes on a limited plane, red is simultaneously applied to all the working electrodes. It is preferable to irradiate with external light.
Moreover, when the dimension of each said working electrode is small, it is preferable to irradiate infrared light to these working electrodes using an infrared microscope.

From the viewpoint of making the measurement conditions between the working electrodes the same, the electrochemical infrared spectrometer includes a multichannel detector capable of simultaneously detecting reflected light emitted from the plurality of working electrodes. It is preferable.
Furthermore, in order to stably maintain the conditions of infrared spectroscopic measurement and to make the measurement conditions between the working electrodes the same, the electrolyte solution, the plurality of working electrodes, and the counter electrode are arranged on one inner wall. It is preferable to circulate in the space which has as a part.

  According to the present invention, since a plurality of electrode surfaces can be measured at the same time, it is efficient without taking the trouble of exchanging a prism provided with an electrode or an electrochemical infrared spectroscopic cell equipped with the prism, In addition, a plurality of samples can be measured under the same conditions. The electrochemical infrared spectroscopic apparatus of the present invention can be suitably used particularly for the study of systematic alloy electrode catalysts.

  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 apparatus comprising: an optical system for detecting the intensity by introducing infrared light totally reflected at the interface to a detector, and A plurality of electrodes are provided.

  Hereinafter, the electrochemical infrared spectrometer of the present invention will be described with reference to FIG. FIG. 1A is a schematic view showing a cross section of one embodiment of an electrochemical infrared spectroscopic cell provided in the electrochemical infrared spectroscopic device of the present invention, and FIG. 1B shows the prism of FIG. 1A viewed from the working electrode side. It is a schematic diagram.

  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. A plurality of working electrodes 2 (16 in FIG. 1) are provided for one prism 1, and each working electrode 2 is arranged without contacting a neighboring working electrode 2 with a certain distance. Yes.

  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, and 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 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, it is preferably used when measuring an infrared absorption spectrum outside the region.

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.

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, a triangular prism shape, and the like can be given. Among them, when using an infrared microscope, a hemisphere is preferable from the viewpoint of narrowing the spot diameter of infrared light to a minute region without defocusing, and when an infrared microscope is not used, a triangular prism or trapezoid Is preferred.
The dimensions of the prism are not particularly limited, and may be appropriately determined in consideration of the measurement wave number region and the number and size of the working electrodes to be provided. Usually, the prism is generally used for an electrochemical infrared spectrometer. It is preferable to use a prism with a large size.

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, or the obtained spectrum may be distorted.

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.

  The film thickness of the metal thin film is preferably about 5 to 100 nm, particularly about 20 to 100 nm in order to ensure sufficient electrical 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 electrochemical infrared spectroscopic apparatus of the present invention is greatly characterized in that a plurality of working electrodes are provided for one prism. A conventional electrochemical infrared spectrometer using ATR-SEIRAS has one working electrode for one prism. When observing a plurality of electrode surfaces under the same conditions, a working electrode is provided. It was necessary to replace the prism every time each electrode was measured, or to replace the electrochemical infrared spectroscopic cell. Furthermore, since fluctuations in the metal composition of the metal thin film constituting the working electrode, dissolution of the metal species of the metal thin film in the electrolytic solution, and the like occur, it is difficult to keep the conditions between a plurality of sample measurements constant.

  On the other hand, the electrochemical infrared spectroscopic device of the present invention is provided with a plurality of working electrodes for one prism, so that the prism provided with the working electrode and the electrochemical infrared including the prism are provided. A plurality of electrode surfaces can be observed at the same time without exchanging the spectroscopic cell, which is efficient. Furthermore, the measurement conditions between a plurality of samples can be made the same. Therefore, according to the present invention, it is possible to systematically observe a plurality of electrode surfaces. Specifically, for example, a plurality of working electrodes having different metal compositions of the metal thin film can be provided on the prism to compare the activity of the alloy electrode catalysts. The activity of the alloy electrocatalyst is significantly affected by fluctuations in the metal composition, changes in the alloy structure, and elution of the metal species, so it is important to measure objectively under the same conditions. This is possible with a spectroscopic device.

The number of working electrodes provided in one prism is not particularly limited. In addition to the number of samples to be measured, the size of the bottom surface (measurement surface) of the prism and the infrared light is condensed on the interface between the prism and the working electrode. What is necessary is just to determine suitably considering the performance of the optical system to make it, the detectability of the detector which detects reflected light, etc. The size of the working electrode also depends on the number of samples to be measured, the size of the bottom surface (measuring surface) of the prism, the performance of the optical system that collects infrared light at the interface between the prism and the working electrode, etc. Is about 10 μm to 5 mm × 10 μm to 5 mm (vertical × horizontal).
The arrangement form of the working electrode is not particularly limited, but when using an infrared microscope, the distance between adjacent working electrodes is more than the limit of spatial resolution of infrared microscope (up to several μm, practically 10 μm or more). Need to be. Further, when an infrared microscope is not used, the distance between adjacent working electrodes needs to be separated by more than the limit of the spatial resolution of the device to be used.

  In the working electrode, the metal composition of the metal thin film may be different for each working electrode, or there may be a plurality of working electrodes made of the metal thin film having the same composition. Moreover, you may provide the working electrode which consists of a metal thin film with the same metal composition and different structures, such as surface structure and thickness.

  The electrochemical infrared spectroscopic apparatus of the present invention is a study of electrode activity of each metal catalyst by using metal thin films having different metal compositions and structures, particularly metal thin films having different metal compositions, as the plurality of working electrodes provided on the prism. And can greatly contribute to the analysis of electrode reactions. On the other hand, by using a metal thin film having the same composition for all working electrodes and controlling the potential of each working electrode, it is possible to observe differences in electrode activity depending on the electrode potential.

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 prism adhesion. 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.

  The method for forming a plurality of working electrodes made of a metal thin film is not particularly limited. For example, when a metal thin film is produced by vacuum deposition, electrolytic plating, electroless plating, sputtering, or the like, a desired size, shape, and arrangement are used. It is possible to use a mask that can form the working electrode, or to use a photolithography method.

Also, 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, and therefore the adhesion of the prism to the metal thin film 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 that passes through the prism 1 and is condensed at 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.

Each working electrode is preferably capable of independently controlling the electrode potential. By controlling the electrode potential of each working electrode independently, in two or more working electrodes made of metal thin films of the same composition, systematic such as differences in electrode activity and electrode reactions due to potential and current differences Observation is possible. In addition, by controlling the electrode potential, it is possible to control the type of electrode reaction, the adsorption phenomenon on the electrode surface, etc., so that the electrode surface can be observed more selectively or integratedly by controlling the electrode potential. Can do. It is also possible to apply a potential suitable for each working electrode.
Furthermore, when the current flowing through each working electrode can be detected independently, voltammetry can be performed in which the current is measured by regulating the electrode potential of each working electrode.

  A potentiostat can be used to control the electrode potential of each working electrode and detect the current. The potentiostat is connected to each working electrode, counter electrode and reference electrode using a suitable lead wire, preferably a lead wire which does not cause an electrochemical reaction in the electrolyte under measurement conditions. Furthermore, the potentiostat is connected to a function generator connected to the multi-channel control device, and controls the electrode potential of each working electrode and detects the current. The multi-channel control device is connected to a personal computer (PC) (see FIG. 3).

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 counter electrode 4 is not particularly limited in material, shape and the like as long as a current can flow through the working electrode 2 to be observed, and one counter electrode may be provided for the plurality of working electrodes 2. 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 in which the electrolytic solution is circulated in the space (conduit 8) having the working electrode and the counter electrode as a part of the inner wall, the electrolytic solution can be used for each action. Since it is difficult to stay in the vicinity of the electrode surface, it is easy to keep the concentration of the electrolyte supplied to each working electrode constant, and the problem that the concentration of the reactant decreases during the measurement is less likely to occur.
In addition, when adopting a flow system, by comparing and observing the working electrode surface arranged on the upstream side of the flow of the electrolyte and the working electrode surface arranged on the downstream side, the composition and life of the electrode reaction product, etc. May be examined. At this time, when each working electrode can control the electrode potential and detect the current independently, more systematic observation and selective observation are possible.

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.
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.

Irradiation of each working electrode with infrared light may be performed by an infrared beam having a size capable of simultaneously irradiating all the working electrodes provided on the prism, or one infrared ray for each working electrode. Beams may be irradiated, or all working electrodes may be divided into a plurality of groups and irradiated for each group.
From the viewpoint of arranging a large number of working electrodes on a limited plane of the prism surface and efficiently measuring the spectrum of each electrode, it is usually preferable to irradiate all working electrodes simultaneously with an infrared beam.

  Irradiation of infrared light to each working electrode requires the use of an infrared microscope depending on the size of the working electrode. Specifically, it is usually necessary to use an infrared microscope when the size of the working electrode is 40 μm × 40 μm or less. In the electrochemical infrared spectroscopic device of the present invention, a plurality of working electrodes are provided for one prism, and an ordinary electrochemical infrared spectroscopic device in which one working electrode is provided for one prism. The size is usually smaller than that of the working electrode, and may be 40 μm × 40 μm or less. Even when the size of each working electrode is larger than 40 μm × 40 μm, an infrared microscope can be used depending on the magnification of the infrared microscope.

The narrowing of the spot diameter of infrared light by an infrared microscope may be appropriately adjusted depending on the shape and size of the working electrode used and the size of the electrode region to be observed. If an infrared microscope is used, the spot diameter of infrared light can be narrowed down to about 10 to 20 μm in principle. As the infrared microscope, a general one used in an infrared microspectroscope may be used, and it varies depending on a spectroscope used in combination. For example, specifically, the size of the working electrode is 40 μm × In the case of 40 μm or less, UMA600 FT-IR Microscope (trade name) manufactured by VARIAN can be used.
On the other hand, as an optical system when the size of the working electrode is larger than 40 μm × 40 μm and no infrared microscope is used, Stingray LS (trade name) manufactured by VARIAN can be used.

The reflected light from the working electrode is detected from the viewpoint of measurement under the same conditions by using a multichannel detector capable of simultaneously detecting the reflected light emitted from each working electrode. Are preferably detected simultaneously. The number of reflected light that can be measured simultaneously by the multichannel detector depends on the detector used. For example, FastImageIR (trade name) manufactured by VARIAN has 32 to 128 channels in length and width, that is, 1024 to 16384. It is possible to simultaneously measure up to 16384 points of reflected light. Further, each channel of the FastImageIR can observe a minimum area of 4 μm square, and in the case of having 64 × 64 channels, the entire detector has (4 μm × 64 channels). ) × (4 μm × 64) = 65536 μm ² region can be observed simultaneously. The area of this simultaneously observable region can be expanded by changing the magnification of the objective mirror. Note that the number of channels of the multichannel detector is not limited to the above range, and may be further increased. As the number of channels increases, the measurable area of each channel may become smaller than 4 μm square.
When simultaneous measurement of the reflected light of each working electrode is impossible, the time interval between each measurement is made as short as possible so that the conditions of each measurement are as identical as possible.

When using a small working electrode of 40 μm × 40 μm or less, that is, when irradiating a minute region with infrared light using an infrared microscope, measurement is difficult unless the detector used is a high-sensitivity detector. A high-sensitivity detector is one that can detect faint light, specifically, a parameter D ^* that represents the sensitivity of the detector is 10 ⁹ or more. As a guideline, an FT-IR spectrometer is used. A semiconductor detector having higher sensitivity than the pyroelectric detector DTGS or TGS installed as a standard can be mentioned. The high-sensitivity detector is usually used while being cooled with liquid nitrogen or helium.
The highly sensitive detector, which is generally used, for example, liquid nitrogen cooling sensitive MCT detector wave number region of 800~4000cm ^-1, InSb detector is measured at 2000 cm ^-1 or more wavenumber region, A bolometer or the like can be used for measurement in a wave number region of 1000 cm ⁻¹ or less.

  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 detector described above, the optical system for detecting the intensity includes a light source for infrared light, a lens, a reflecting mirror for generating and extracting parallel light and convergent light from the emitted light, a slit, etc. These 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. In the case of using an infrared microscope or image measurement, infrared light is transmitted from a spectroscope to an infrared microscope (see FIG. 4 (4B)) or an external optical system for image measurement (see FIG. 5) using a plane mirror. Lead.

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.
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 device of the present invention enables detailed elucidation of the electrode reaction mechanism in the electrode surface, for example, the catalyst surface of a fuel cell, the device utilizing electrochemistry, and the reaction (reaction distribution) propagating on the electrode surface. It is to make. Furthermore, it can also be suitably used for observation of plating processes, metal corrosion, various surface treatments, and the like. In addition, the electrochemical spectroscopic device of the present invention can visualize (imaging) the presence, position, and distribution of chemical species on the electrode surface.

(Reference experiment example)
An electrochemical infrared spectroscopic cell in which a platinum thin film serving as a working electrode was formed on a Si prism on a triangular prism as shown in FIG. 5 (5A) was prepared. In order to prevent leakage of the electrolytic solution (a solution of carbon monoxide gas in sulfuric acid), an O-ring was interposed between the Si prism and the container containing the electrolytic solution.

6 (6A) is a view of the working electrode of FIG. 5 (5A) as viewed from the upper surface side (the side opposite to the prism). As shown in FIG. 6 (6A), the working electrode (platinum thin film) is formed on the surface of the Si prism at a size of 3.5 mm × 3.5 mm, and the working electrode is connected to a platinum lead wire connected to a potentiostat. The electrode potential was controlled and the current was detected. In FIG. 6 (6A), a circular black portion surrounding the working electrode is a portion where the Si prism is exposed. The inner part of the O-ring contacts the electrolyte.
FIG. 6 (6B) is a photograph of the actually used Si prism and working electrode. The photograph shows a state before a container or the like for storing an electrolytic solution is installed, and its surface is covered with distilled water to prevent contamination of the working electrode.

  The working electrode was irradiated with infrared light without using an infrared microscope, and reflected light enhanced by the SEIRA effect was obtained by using a multi-channel MCT detector having a 64 × 64 channel FPA (Focal Plane Array). . FIG. 5 (5B) shows a conceptual diagram of a multi-channel MCT detector. A spectrum is stored in each of 64 × 64 FPAs.

FIG. 7 shows a spectrum of a minute region (40 μm × 40 μm) of the working electrode obtained by the (38, 38) channel. A large peak of CO was observed at 2050 cm ⁻¹ . This shows that CO is adsorbed on the surface of the Pt electrode.
FIG. 8 shows a two-dimensional distribution of CO 2050 cm ⁻¹ band intensity. The two-dimensional distribution of FIG. 8 was obtained by plotting the band intensity of the spectrum detected by each FPA. In FIG. 8, the portion where the color density is high is the portion where the CO coverage is high. Since CO adsorbs only on the platinum surface, an image corresponding to a 3.5 mm × 3.5 mm working electrode and a platinum lead wire was obtained. The reason why the image is not square is that infrared light is incident obliquely from left to right, and digital correction is possible.

  Based on the above results, it is possible to measure the spectrum of chemical species present in a specific minute region (40 μm × 40 μm) on the surface of the working electrode (3.5 mm × 3.5 mm), and to provide a single prism surface. It can be seen that it is possible to obtain a two-dimensional distribution of chemical species present near the surface of the working electrode. Thus, as in the present invention, a plurality of working electrodes are provided for one prism, the working electrodes are irradiated with infrared light, reflected light is detected, and chemical species present near the surface of each working electrode are detected. It was shown that it is possible to observe at the same time.

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 schematic diagram which shows the connection form of a potentiostat. It is the schematic which shows the example of 1 form of the electrochemical infrared spectroscopy apparatus of this invention. It is a conceptual diagram which shows the external optical system for image measurement provided with the electrochemical infrared spectroscopy cell used in the reference experiment example of this invention. It is the figure (6A) and the photograph (6B) which looked at the working electrode provided on the prism in the reference experiment example of this invention from the upper surface (opposite side to a prism). It is a spectrum of the micro area | region on the working electrode in the reference experiment example of this invention. It is a figure which shows the two-dimensional distribution of the band intensity of 2050cm < ^-1 > of CO adsorb | sucked to the surface of the working electrode in the reference experiment example 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. It is a schematic diagram which shows one form of the electrochemical infrared spectroscopy cell used for the conventional ATR-SEIRAS 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 (8)

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 bottom surface of the prism; 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;
An electrochemical infrared spectroscopic apparatus comprising a plurality of the working electrodes for one prism.   2. The electrochemical infrared spectrometer according to claim 1, wherein at least one of the plurality of working electrodes is made of a metal thin film having a metal composition different from that of at least one other working electrode.   The electrochemical infrared spectrometer according to claim 1 or 2, wherein the plurality of working electrodes can independently control an electrode potential.   The electrochemical infrared spectrometer according to any one of claims 1 to 3, wherein each of the plurality of working electrodes can independently detect a current flowing through the working electrode.   5. The electrochemical infrared spectrometer according to claim 1, wherein the plurality of working electrodes are irradiated with infrared light simultaneously on all the working electrodes.   The electrochemical infrared spectrometer according to claim 1, wherein the plurality of working electrodes are irradiated with infrared light from an infrared microscope.   The electrochemical infrared spectrometer according to any one of claims 1 to 6, further comprising a multichannel detector capable of simultaneously detecting reflected light emitted from the plurality of working electrodes. The electrochemical infrared spectroscopic apparatus according to any one of claims 1 to 7, wherein the electrolytic solution circulates in a space having the plurality of working electrodes and the counter electrode as part of an inner wall.

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