Patent Application
20140346052
The present invention relates to a reaction vessel for Raman spectrophotometry and a Raman spectrophotometry method using the same, and more particularly, to Raman spectrophotometry under an electrochemical reaction.
A chemical reaction in which a solid surface is involved relates to various important applications in industrial aspects, such as batteries, catalysts, coating, fine particle formation, corrosion, sensors, and the like. However, a reaction situation of the chemical reaction that takes place at the solid surface is hard to study, compared to a uniform reaction system that takes place in a solution or in a gas.
For this reason, laser Raman spectroscopy is employed. Laser Raman spectroscopy is a method for estimating a chemical structure of a molecule by measuring an oscillation state of the molecule. Unlike infrared spectroscopy that provides similar information, laser Raman spectroscopy has an advantage in that a measurement is possible even in a solution including a water solution. Therefore, with laser Raman spectroscopy, a chemical reaction process at a solid surface surrounded by a solution can be tracked at a molecular level (for example, see Non Patent Literature 1).
[NPL 1] Surface Technology Vol. 57 (2006), No. 11, pp 793-798
However, when an electrochemical reaction of a sample is performed at a solid surface in an electrolyte solution, for example, it is preferred for a member which can affect the electrochemical reaction, such as a wiring line for electrically connecting a working electrode and an external power source, to not exist in the electrolyte solution in a reaction vessel storing the electrolyte solution and the sample.
The present invention has been achieved in view of the above aspects, and it is one of the objects of the present invention to provide a reaction vessel for Raman spectrophotometry and a Raman spectrophotometry method using the same, which are suitable for an electrochemical reaction at a solid surface in an electrolyte solution.
In order to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided a reaction vessel for Raman spectrophotometry, including: a housing portion including a transparent window portion, in which a hollow portion for storing an electrolyte solution is formed; and a working electrode portion configured from a conductive material that is electrochemically inactive in the electrolyte solution, the working electrode portion including: one part arranged facing the transparent window portion in the hollow portion to hold a sample; and another part extended to outside the housing portion to be connected to an external power source thereto. According to one embodiment of the present invention, a reaction vessel for Raman spectrophotometry, which is suitable for the electrochemical reaction at the solid surface in the electrolyte solution, is provided.
Further, the working electrode portion may be a member that extends parallel to the transparent window portion. Further, the conductive material may be at least one material selected from a group consisting of a conductive carbon material, a conductive ceramic, gold, and a gold-plated conductive material. Further, the reaction vessel may be used in microscopic Raman spectrophotometry.
In order to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided a Raman spectrophotometry method, including: preparing a reaction vessel including: a housing portion including a transparent window portion, in which a hollow portion for storing an electrolyte solution is formed; and a working electrode portion configured from a conductive material that is electrochemically inactive in the electrolyte solution, the working electrode portion including one part arranged facing the transparent window portion in the hollow portion and another part extended to outside the housing portion; holding a sample on the one part of the working electrode portion arranged facing the transparent window portion; connecting the other part of the working electrode portion extended to outside the housing portion to an external power source; storing the electrolyte solution in the hollow portion; and performing Raman spectrophotometry in an electrochemical reaction of the sample in the electrolyte solution. According to one embodiment of the present invention, a Raman spectrophotometry method, which is suitable for the electrochemical reaction at the solid surface in the electrolyte solution, is provided.
Further, the working electrode portion may be a member that extends parallel to the transparent window portion. Further, the conductive material may be at least one material selected from a group consisting of a conductive carbon material, a conductive ceramic, gold, and a gold-plated conductive material.
Further, in the above-mentioned method, the Raman spectrophotometry may be microscopic Raman spectrophotometry. In this case, the microscopic Raman spectrophotometry may be performed in a situation where the reaction vessel is arranged between a lens for radiating excitation light and a microscope stage arranged facing the lens.
According to one embodiment of the present invention, a reaction vessel for Raman spectrophotometry and a Raman spectrophotometry method using the same, which are suitable for the electrochemical reaction at the solid surface in the electrolyte solution, are provided.
An exemplary embodiment of the present invention is described below. It should be noted that the present invention is not limited to examples described in the embodiment.
As illustrated in
The present reaction vessel 1 is used for Raman spectrophotometry of an electrochemical reaction at a solid surface (specifically, a surface 21a of the sample stage part 21 of the working electrode portion 20 facing the window portion 11) in the electrolyte solution E. The electrochemical reaction is not particularly limited as long as the electrochemical reaction takes place at the solid surface in the electrolyte solution E, and for example, the electrochemical reaction may be a redox reaction. Further, the present reaction vessel 1 may also be used for Raman spectrophotometry in, for example, an electrochemical polymerization process, a crystal deposition process, an electrical reaction process, an electrochemical synthesis process, a sensor reaction process, and a biochemical reaction process.
Further, the electrochemical reaction may be, for example, a heterogeneous catalyst reaction. That is, in this case, a sample S containing a heterogeneous catalyst is used. More specifically, the sample S containing the heterogeneous catalyst is held on the sample stage part 21 of the working electrode portion 20 of the present reaction vessel 1. The Raman spectrophotometry is then performed in the electrolyte solution E on the heterogeneous catalyst reaction (for example, a catalytic redox reaction by the heterogeneous catalyst) on the sample stage part 21 of the working electrode portion 20.
The heterogeneous catalyst is not particularly limited, but for example, at least one catalyst selected from a group consisting of carbon catalyst, immobilized catalyst such as metal catalyst, metal compound catalyst, and the like, and immobilized biomolecule (biomolecule working as immobilized sensor) such as immobilized antigen, immobilized antibody, immobilized nucleic acid, immobilized enzyme, and the like maybe used. As the carbon catalyst, for example, a carbon catalyst configured from a carbonized material obtained by carbonizing a raw material including an organic substance and a metal (preferably transition metal) and exhibiting a redox reaction catalytic activity (for example, an oxygen reduction reaction catalytic activity) may be used.
The electrolyte solution E is not particularly limited as long as an electrochemical reaction of the sample S proceeds in the electrolyte solution E. That is, pH of the electrolyte solution E is not limited, and thus an acidic electrolyte solution E may be used or an alkaline electrolyte solution E may be used. Further, as the electrolyte solution E, a corrosive electrolyte solution may also be used.
When the electrolyte solution E is acidic, the pH thereof may be, for example, from 0 to 5. The acidic electrolyte solution E may be selected from, for example, a group consisting of a mineral acid such as sulfuric acid, nitric acid, hydrochloric acid, or perchloric acid, a super strong acid, an organic acid, an organic electrolyte, a buffer, and an ionic liquid.
The housing portion 10 is a box-shaped hollow member that stores therein at least the electrolyte solution E and the sample stage part 21 of the working electrode portion 20. In the example illustrated in
A material constituting the housing portion 10 is not particularly limited as long as the material is an insulating material, and for example, at least one material selected from a group consisting of a resin, a metal coated with an insulating liner, a ceramic, and glass may be used.
When the corrosive electrolyte solution E (for example, an acidic electrolyte solution E) is used, it is preferred that the housing portion 10 be configured from a corrosion-resistant material. In this case, as the resin, there may be preferably used, for example, at least one material selected from a group consisting of a vinyl chloride resin, a phenol resin, a polyolefin resin (such as polyethylene and/or polypropylene), an acrylic resin, a fluororesin, and a silicone resin.
The window portion 11 constitutes a part of an outer wall of the housing portion 10, through which excitation light (laser) passes in the Raman spectrophotometry. In the example illustrated in
The hollow portion 12 is a space formed inside the housing portion 10 for storing therein the electrolyte solution E. It is preferred that the hollow portion 12 is a sealed space at least at the time of performing the Raman spectrophotometry.
The working electrode portion 20 includes the sample stage part 21 arranged inside the hollow portion 12 of the housing portion 10 and the extended part 22 extended to outside the housing portion 10.
A shape of the working electrode portion 20 is not particularly limited as long as the shape is in a range where the Raman. spectrophotometry can be performed on the electrochemical reaction using the working electrode portion 20 as a working electrode, and for example, the working electrode portion 20 may be a member that extends parallel to the window portion 11 (for example, a plate-shaped member illustrated in
In this case, because the sample stage part 21 and the extended part 22 are formed as one part and another part of the member extending parallel to the window portion 11, a height of the present reaction vessel 1 (particularly a height of the housing portion 10) is effectively reduced. A thickness of the working electrode portion 20 is not particularly limited.
The conductive material constituting the working electrode portion 20 is a material having conductivity and being electrochemically inactive in the electrolyte solution E. The fact that the conductive material is electrochemically inactive includes, for example, that the conductive material is not dissolved when a potential is applied to the conductive material, and that the conductive material does not exhibit an electrolysis of a solvent (electrolyte solution) in contact with the conductive material in a broad potential range. That is, the conductive material is, for example, a conductive material that is electrochemically inactive in the electrolyte solution E in a range from −0.2 V to 1.2 V (vs. NHE) regardless of pH of the electrolyte solution E.
The conductive material is not particularly limited as long as the conductive material is electrochemically inactive in the electrolyte solution E, and for example, at least one material selected from a group consisting of a conductive carbon material, a conductive ceramic, gold, and a gold-plated conductive material may be used.
The conductive carbon material is not particularly limited as long as the conductive carbon material is a carbon material having conductivity, and for example, at least one material selected from a group consisting of glass-type carbon, isotropic carbon, and a graphite material (for example, HOPG) may be used. The conductive ceramic is not particularly limited as long as the conductive ceramic is a ceramic material having conductivity, and for example, at least one material selected from a group consisting of titanium oxide, tin oxide, and indium tin oxide (ITO) may be used.
The sample stage part 21 is a part of the working electrode portion 20 arranged facing the window portion 11 in the hollow portion 12 of the housing portion 10. The sample S is held on the surface 21a of the sample stage part 21 facing the window portion 11. In the example illustrated in
The extended part 22 is a part of the working electrode portion 20, which is different from the sample stage part 21, arranged protruding from an outer surface 10a of the housing portion 10. That is, the extended part 22 is formed by causing a part of the working electrode portion 20 to penetrate through the housing portion 10 from inside the hollow portion 12, and extending the part to outside the housing portion 10.
More specifically, for example, when the working electrode portion 20 is a member that extends parallel to the window portion 11, the extended part 22 is formed by extending a part of the member to outside the housing portion 10 parallel to the window portion 11. In the example illustrated in
At the time of performing the Raman spectrophotometry, the extended part 22 is electrically connected to the external power source. That is, in the example illustrated in
The present reaction vessel 1 includes the extended part 22 that is formed by extending a part of the working electrode portion 20 to outside the housing portion 10 as a terminal for connecting to the external power source, and hence it is not necessary to arrange the wiring W for establishing an electrical connection to the external power source in the electrolyte solution E.
Therefore, existence of a member that affects the electrochemical reaction in the electrolyte solution E in the present reaction vessel 1 is effectively reduced. In addition, a structure of the present reaction vessel 1 is simplified.
In related-art microscopic Raman spectrophotometry, when a reaction vessel to be used cannot be arranged in a small space between an objective lens and a microscope stage of a commercially available microscopic Raman spectrophotometry system, it has been necessary to modify the microscopic Raman spectrophotometry system when performing the microscopic Raman spectrophotometry. However, the present reaction vessel 1 has the above-mentioned structure, and hence the height thereof is effectively reduced, compared to the related-art reaction vessel for Raman spectrophotometry.
Therefore, the present reaction vessel 1 is preferably used for the microscopic Raman spectrophotometry. That is, as illustrated in
In addition, as illustrated in
In the example illustrated in
Further, the end part 31 of the counter electrode 30 and the end part 41 of the reference electrode 40 may be protruded from another outer surface 10b formed in a direction different from the outer surface 10a of the housing portion 10 through which the extended part 22 of the working electrode portion 20 is protruded (in the example illustrated in
In addition, as illustrated in
Therefore, in the hollow portion 12, the working electrode portion 20 may be arranged close to the window portion 11, and more electrolyte solution E may be stored in a space between the window portion 11 and the bottom portion 14 than in a space between the window portion 11 and the working electrode portion 20. Further, in the example illustrated in
A Raman spectrophotometry method according to this embodiment (hereinafter referred to as “present method”) is a method of performing Raman spectrophotometry by using the above-mentioned present reaction vessel 1. That is, the present method includes: preparing a reaction vessel (present reaction vessel 1) including the housing portion 10 including the window portion 11, in which the hollow portion 12 for storing the electrolyte solution E is formed, and the working electrode portion 20 configured from the conductive material that is electrochemically inactive in the electrolyte solution E and including one part (sample stage part 21) arranged facing the window portion 11 in the hollow portion 12 and another part (extended part 22) extended to outside the housing portion 10; holding the sample S on the sample stage part 21; connecting the extended part 22 to the external power source; storing the electrolyte solution E in the hollow portion 12; and performing the Raman spectrophotometry of the electrochemical reaction of the sample S in the electrolyte solution E.
Here a case where the microscopic Raman spectrophotometry is performed as illustrated in
Specifically, as illustrated in
A method of holding the sample S on the sample stage part 21 is not particularly limited as long as the sample S is fixed on the surface 21a of the sample stage part 21. That is, for example, the sample S may be fixed on the surface 21a by using a method of applying slurry that contains the sample S on the surface 21a of the sample stage part 21 with use of a binder (for example, Nafion (trade mark)) or a method of directly depositing the sample S on the surface 21a of the sample stage part 21.
A method of connecting the extended part 22 to the external power source is not particularly limited as long as the extended part 22 is electrically connected to the external power source. That is, for example, as illustrated in
The external power source is not particularly limited as long as the external power source applies a potential to the working electrode portion 20, and for example, a potentiostat may be preferably used.
Storing of the electrolyte solution E in the hollow portion 12 is not particularly limited as long as the sample stage part 21 of the working electrode portion 20 is immersed in the electrolyte solution E. That is, for example, the sealed hollow portion 12 may be filled with the electrolyte solution E in such a manner that a gaseous phase is not substantially formed in the hollow portion 12.
In the Raman spectrophotometry, firstly, a potential is applied from the external power source to the working electrode portion 20 via the extended part 22, to thereby start the electrochemical reaction of the sample S held on the sample stage part 21. The sample S is then irradiated with the excitation light from the lens L of the Raman spectrophotometry system via the window portion 11, and Raman-scattered light emitted in response to the electrochemical reaction of the sample S on the surface 21a of the sample stage part 21 is guided to an optical system of the Raman spectrophotometry system in a backward scattering mode, to thereby obtain the Raman spectra.
In this manner, in the present method, in-situ Raman spectrophotometry (in the example illustrated in
[Preparation of Carbon Catalyst]
As the heterogeneous catalyst, a carbon catalyst configured from a carbonized material obtained by carbonizing a raw material including an organic substance and a metal was prepared.
Firstly, the raw material to be carbonized was prepared. That is, phenol resin (for fiber spinning, manufactured by Gun Ei Chemical Industry Co., Ltd.) and cobalt phthalocyanine (90% purity, manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed in acetone such that a weight percentage of cobalt with respect to the phenol resin was 3 wt %. The obtained mixture was stirred by an ultrasonic wave for 30 minutes, and the solvent was removed by using an evaporator. Thereafter, the mixture was dried under reduced pressure for a night at a temperature of 70° C., and thus the raw material was obtained.
Subsequently, the raw material was carbonized. That is, the raw material of 1 g was placed on a silica boat, and the silica boat was placed at the center of a silica reaction tube (φ23.5 mm×600 mm). A high-purity nitrogen gas was then purged in the silica reaction tube at a flow rate of 500 mL/min for 20 minutes. Thereafter, the silica reaction tube was heated under the flow of the high-purity nitrogen gas (500 mL/min) by using an infrared image furnace (RHL410P, manufactured by Shinku-Riko. Inc.), and the temperature thereof was raised up to 1,000° C. at a temperature rise rate of 10° C./min. The silica reaction tube was then maintained at 1,000° C. for an hour to carbonize the raw material, and thus the carbonized material was obtained.
The carbonized material was pulverized by using a mortar, the pulverized carbonized material of 500 mg and 10 pulverizing balls were inserted in a vessel, and a pulverizing process was further performed at a rotation speed of 750 rpm for 90 minutes by using a planetary ball mill. Thereafter, the pulverized carbonized material was sifted by using a sifter having a screen size of 106 μm, and the carbonized material that passed through the sifter was collected.
The carbonized material, a concentrated hydrochloric acid, and a stirrer were put into a vial and stirred for two hours by using a magnetic stirrer, and a suction filtration was further performed. This operation was repeated three times, and then the carbonized material was dried under reduced pressure for a night at a temperature of 80° C. The dried carbonized material was finally obtained as the carbon catalyst. It has been confirmed that this carbon catalyst exhibits a redox catalytic activity such as an oxygen reduction catalytic activity.
[Assembly of Reaction Vessel]
Firstly, slurry containing the carbon catalyst (catalyst slurry) was prepared. That is, about 5.0 mg of the carbon catalyst was put into a plastic vial. Subsequently, glass beads (BZ-1, φ0.991 mm to φ1.397 mm, manufactured by AS ONE Corporation) of one spoonful of microspatula, 50 μL of 5% Nafion (trade mark) dispersed solution, 150 μL of ethanol (special grade reagent), and 150 μL of ultrapure water were added in the vial. The obtained composition was treated for 15 minutes by using an ultrasonic wave, and then the catalyst slurry was obtained.
Subsequently, the catalyst slurry was applied on the sample stage part 21 of the working electrode portion 20. As the working electrode portion 20, a plate-shaped member of the glass-type carbon (30 mm×10 mm×0.5 mm, manufactured by Nisshinbo Chemical Inc.) was used. The catalyst slurry of 19.8 μL was applied on the surface 21a of the sample stage part 21, which is a part on one end side of the glass-type carbon plate, and the applied catalyst slurry was dried in a desiccator under a wet condition, to thereby fix the sample S containing the carbon catalyst on an area of 1.4 cm2 range of the surface 21a.
The present reaction vessel 1 illustrated in
The working electrode portion 20 on which the sample S was held in the above manner, the counter electrode 30 (Pt line), and the reference electrode 40 of Ag/AgCl (RE-3VP, screw-in reference electrode, manufactured by BAS Inc.) were then mounted on the housing portion 10 as illustrated in
The hollow portion 12 of the housing portion 10 was filled with the electrolyte solution E (sulfuric acid aqueous solution, 0.5MH2SO4) in such a manner that a gaseous phase was not formed in the hollow portion 12, and then the hollow portion 12 was sealed. Before filling the electrolyte solution E in the hollow portion 12 of the present reaction vessel 1, dissolved oxygen in the electrolyte solution E was purged by performing bubbling of a nitrogen gas for 30 minutes.
The distance between the window portion 11 and the sample stage part 21 of the working electrode portion 20 was 2 mm. That is, a layer of the electrolyte solution E having a thickness of 2 mm was formed between the window portion 11 and the sample stage part 21. In addition, the present reaction vessel 1 was designed such that the sample S fixed on the sample stage part 21 of the working electrode portion 20 was arranged at a focal position of an optical system included in the commercially available microscopic laser Raman spectrophotometry system to be described later.
[Cyclic Voltammetry]
In order to confirm that the present reaction vessel 1 prepared in the above manner works normally as an electrochemical device, cyclic voltammetry (CV) was performed by using a potentiostat (ALS700 series electrochemical analyzer, manufactured by BAS Inc.). As the electrolyte solution E, a sulfuric acid solution (0.5MH2SO4) with nitrogen saturated was used.
A cyclic voltammogram was then obtained by performing a CV measurement with an initial potential set to a natural potential, a scanning range set to 0 V to 1.0 V (vs. NHE), a scanning speed set to 50 mV/s, and the number of cycles set to 5 cycles.
For comparison, as a related-art method, cyclic voltammetry was performed under a similar condition except that a three-electrode type electrochemical cell was used as a substitute for the present reaction vessel 1. Specifically, the catalyst slurry of 4 μL prepared in the same manner as the above-mentioned Example 1 was applied on a disk electrode (glassy carbon, φ6 mm) and dried in a desiccator under a wet condition. After drying, this disk electrode was mounted on a rotary ring disk electrode measurement device. The sulfuric acid aqueous solution (0.5MH2SO4) was used as the electrolyte solution, a reversible hydrogen electrode (RHE) was used as the reference electrode, and a carbon electrode was used as the counter electrode. Before mounting the disk electrode on the measurement device, bubbling of a nitrogen gas was performed for 30 minutes on the electrolyte solution in the electrolyte cell. Thereafter, a cyclic voltammogram was obtained by performing a CV measurement with an initial potential set to a natural potential, a scanning range set to 0 V to 1.0 V (vs. NHE), a scanning speed set to 50 mV/s, and the number of cycles set to 5 cycles by using the potentiostat (ALS700 series electrochemical analyzer, manufactured by BAS Inc.).
The obtained cyclic voltammogram is shown in
Although it is omitted from drawing, chronoamperometry by using the present reaction vessel 1 also obtained substantially the same result as the one obtained by using the related-art method. That is, it was confirmed that the present reaction vessel 1 worked normally as an electrochemical device.
[Raman Spectrophotometry]
In-situ microscopic laser Raman spectrophotometry was performed by using a commercially available microscopic laser Raman spectrophotometry system (microscopic laser Raman system Nicolet Almega XR, manufactured by Thermo Fisher Scientific Inc.) and the present reaction vessel 1.
That is, the present reaction vessel 1 prepared in the above manner was arranged just below an objective lens (corresponding to the lens L illustrated in
The in-situ microscopic Raman spectrophotometry of the electrochemical reaction was then performed in a backward scattering mode by connecting the present reaction vessel 1 to a potentiostat, starting an electrochemical reaction in the electrolyte solution E by maintaining a potential at 2.0 V (vs. NHE), and irradiating the sample S with the excitation light (laser) via the window portion 11.
As an excitation light source, an Ar laser having a wavelength of 532 nm was used. An output of the excitation light was set to be 2 mW at the surface of the sample S. As the objective lens, a long focal-length lens having a magnification of 50 times was used. An exposing time period was set to 60 seconds, the number of times of exposing was set to 4, the number of times of background exposing was set to 16, and an aperture was set to a pin hole of 25 μm. The measurement was performed at six points on the sample S that were selected at random.
The obtained Raman spectra are shown in
As shown in
A result of evaluating the intensity of the D band (peak intensity at 1,358 cm−1) in the Raman spectra shown in
It is considered that the temporal increase of the intensity of the Raman band, which is unique to such a carbon structure, reflects a process in which the carbon structure of the carbon catalyst contained in the sample S is oxidized in the electrolyte solution E. That is, in general, a Raman activity is increased as the crystallinity of the carbon structure is increased and a larger Raman peak is obtained, and hence it is considered that, for example, a portion where the crystallinity is low in the carbon structure of the carbon catalyst is decreased due to the oxidation and a portion where the crystallinity is high is increased, so that the Raman activity is increased.
Further, for example, when the carbon catalyst is oxidized due to the application of the potential in the electrolyte solution E, the carbon catalyst is taken out from the electrolyte solution E, and its carbon structure is analyzed, it is not possible to discriminate whether the oxidation of the analyzed carbon structure is due to the application of the potential or due to contact with air after the carbon catalyst is taken out from the electrolyte solution.
In contrast to this, in this embodiment, because the change of the carbon structure of the carbon catalyst due to the application of the potential in the electrolyte solution E is analyzed by in-situ Raman spectrophotometry, the Raman spectra is obtained as a useful result which directly reflects the oxidation process due to the application of the potential.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-257849 | Nov 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/078386 | 11/1/2012 | WO | 00 | 5/21/2014 |
