JP2013200123A - Cell for electrochemical measurement and electrochemical measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell for electrochemical measurement and an electrochemical measurement system, which are favourable for the observation of a sample, for example, a fuel cell electrode catalyst such as Pt catalyst.SOLUTION: A cell for electrochemical measurement 10 comprises: a base plate 3 including an electron beam transmissive thin film 1 and a stiffened plate 2; an electrode pair including a gold electrode 5 and a platinum electrode 4 that are mounted on the thin film 1 of the base plate 3; a surrounding frame 6 surrounding the electrode pair on the thin film 1; an electrolytic solution ES sealing the electrode pair in a space that is surrounded on the thin film 1 by the surrounding frame 6; a lid 9 arranged above the surrounding frame 6 and including an electron beam transmissive thin film 7 and a stiffened plate 8. Observation windows 8a and 2a are formed by hollowing respective positions of the stiffened plates 8 and 2 of both the lid 9 and the base plate 3, each corresponding to the gold electrode 5. A sample S in contact with the gold electrode 5 can be observed through the observation windows 8a and 2a, and an electron beam EB can penetrate the corresponding observation windows 8a and 2a and the sample S between the observation windows.

Description

  The present invention relates to an electrochemical measurement system for observing an electrochemical change of a sample, and an electrochemical measurement cell included in the measurement system.

  For example, knowing the mechanism of synthesis, activity, and deterioration of a catalyst for a fuel cell is an important guideline for developing a new catalyst.

  By the way, although a sample in a solution can be observed in-situ by TEM (transmission electron microscope), the potential of the sample cannot be measured. For example, a catalyst sample for a fuel cell is eluted. The current situation is that the potential to start cannot be precisely confirmed. In addition, the low resolution at the time of observation is also a factor that inhibits the potential confirmation of catalyst elution.

  To analyze the cause of the above problem, it is possible to measure the potential by placing a sample on the electrode, but the electron beam cannot be transmitted because the sample is placed on the electrode. The inability to do so is the biggest factor.

  On the other hand, regarding the resolution, in the cell into which the liquid is injected, the electron beam is easily absorbed by the liquid and the observation window, and as a result, the resolution is lowered.

  While solving these problems, the present inventors mainly used a transmission electron microscope for the main purpose of observing in real time electrochemical changes of electrode catalysts for fuel cells such as Pt catalysts as samples. We have been developing electrochemical measurement cells for observation.

  Here, Patent Document 1 discloses a method in which an ionic liquid is held by a sample holding member having an opening, a sample is put therein, the sample is floated in the ionic liquid, and observed with a transmission electron microscope. Yes. According to this observation method, the shape of the sample itself can be observed without deforming the sample. However, since it is not intended for observing electrochemical changes in electrode catalysts for fuel cells such as Pt catalysts, the cell configuration is not suitable for observing electrochemical changes in the electrode catalyst. . Specifically, since the electrode material is not clear, it is unclear whether or not the electrochemical change of the Pt catalyst can be observed, and it is not configured to allow transmission of an electron beam with the sample catalyst in contact with the electrode. In addition, it is unclear whether or not the electrochemical change of the sample catalyst can be observed.

JP 2009-266741 A

  The present invention has been made in view of the above-described problems. For example, an electrochemical measurement cell and electrochemical measurement suitable for observing electrochemical changes in a sample including an electrode catalyst for a fuel cell such as a Pt catalyst. The purpose is to provide a system.

  In order to achieve the above object, an electrochemical measurement cell according to the present invention is an electrochemical measurement cell, and is placed on a substrate made of an electron beam-permeable thin film and a stiffening plate, and on the thin film of the substrate. An electrode pair composed of a gold electrode and a platinum electrode, an enclosure frame that surrounds the electrode pair on the thin film, an electrolyte solution that seals the electrode pair in a space on the thin film surrounded by the enclosure frame, and an upper part of the enclosure frame A lid formed of an electron beam transmissive thin film and a stiffening plate, and the stiffening plates of both the lid and the substrate are cut out at positions corresponding to the gold electrodes. The observation window is formed so that the sample in contact with the gold electrode can be confirmed from the observation window, and the electron beam can pass through the corresponding observation window and the sample in between.

  The electrochemical measurement cell of the present invention is an electrode catalyst whose measurement object is mainly composed of Pt for fuel cells, etc., and is a cell used for TEM observation, and its plane dimension is about several mm square or less. It is a size. Of course, the sample to be observed is not limited to the electrode catalyst for fuel cells.

  The substrate is composed of an electron beam transmissive thin film and a stiffening plate. The thin film is preferably made of silicon nitride, silicon dioxide, amorphous silicon (for example, polysilicon), etc., and its thickness is preferably at most several tens of nm, for example, 10 nm. About 20 nm is desirable. Further, the stiffening plate for forming the substrate by imparting rigidity to the electron beam permeable thin film is preferably made of silicon or the like.

  On the thin film which comprises a board | substrate, the electrode pair which consists of a gold electrode and a platinum electrode or a plurality of pairs is formed.

  Among the electrode pairs, the gold electrode comes into contact with the sample to be observed, and an electrochemical change after application of current to the electrode pair of the sample in contact with the gold electrode is observed. In this way, by using the gold electrode as the electrode for contacting the sample to observe the electrochemical change, the electrode is electrically stable and measurement noise can be reduced.

  In addition, when using Pt (platinum) or its alloy, which is frequently used as an electrode catalyst for fuel cells, as a sample, a gold electrode is suitable for observing the change by bringing it into contact.

  On the other hand, when the other electrode constituting the electrode pair is a platinum electrode, hydrogen can be generated on the electrode to form a reversible hydrogen electrode.

  Further, in order to fill the electrode pair with the electrolytic solution, a surrounding frame is provided so as to surround the electrode pair on the thin film, and the electrolytic solution is filled in the surrounding frame. In addition, perchloric acid, a sulfuric acid, nitric acid etc. can be used for this electrolyte solution.

  The plane dimension of the electrochemical measurement cell is about several mm square, and it is necessary to prevent the electrode pair from being short-circuited in such an extremely small cell. Therefore, the enclosure frame is made of ceramics such as silicon dioxide. Is good. In the case where the enclosure frame is formed from a rubber material for sealing, it can be said that the enclosure frame of the ceramic material is preferable because the rubber may melt and change the components of the electrolytic solution.

  Above the enclosure frame, a lid of the same combination as the substrate, i.e., a lid made of an electron beam permeable thin film and a stiffening plate, is disposed, and the substrate and the enclosure frame, and the lid and the enclosure frame are liquid-tight. It is connected (sealed) to form an electrochemical measurement cell.

  In this electrochemical measurement cell, the stiffening plates on both the lid and the substrate are both cut through the positions corresponding to the gold electrodes to form an observation window, and the sample in contact with the gold electrode is confirmed from the observation window. In addition, the electron beam can pass through the corresponding observation window and the sample between them.

  With such a configuration, it is possible to confirm the electrochemical change of the sample in contact with the electrode while transmitting the electron beam through the observation window.

  Actually, this electrochemical measurement cell is fixed to the tip of the holder, installed in the transmission electron microscope, and the electrochemical change of the sample is monitored by a CCD camera or the like constituting the transmission electron microscope. become.

  Note that, for example, a substrate or a lid may be configured by fitting an electron beam transmissive thin film into a groove (observation window) formed in a stiffening plate. In this embodiment, a thin film is formed in a small-sized groove. Since it is inevitable that it takes a lot of time and labor to produce the film, it is not preferable.

  In the surrounding frame, it is preferable that the inner surface facing the electrode pair is formed of either a curved surface or a surface in which a flat surface and a curved surface are continuous.

  When the enclosure is made of silicon dioxide or the like and the electrolyte is filled with the electrolyte, the surroundings of the electrolyte are generally hydrophobic, so if there are corners on the inner surface of the enclosure, gas will accumulate there. It becomes easy. There is also a measure to eliminate the ease of gas accumulation by introducing a hydrophilic drug into the electrolyte, but in this case there is a concern that the hydrophilic drug may affect the electrochemical measurement. It is preferable to improve the inner shape of the surrounding frame so that it does not have a corner portion as in this embodiment.

  Further, the planar shape of the observation window is preferably circular. Since the inside of the transmission electron microscope is an ultra-high vacuum atmosphere, while the inside of the cell is an atmospheric atmosphere, an observation window structure that can withstand this pressure difference is required.

  Specifically, the observation window of the thin film formed by hollowing out the stiffener plate of the lid or the substrate is strongly outward with the cutout contour of the stiffener plate as an edge in the ultrahigh vacuum atmosphere of the transmission electron microscope. It will be pulled (sucked).

  At this time, if the contour edge is linear or polygonal, the thin film tends to crack starting from the corner.

  On the other hand, by making the contour edge (contour of the observation window) circular, there is no corner angle that is likely to be the starting point of a crack, and in addition, the tensile force acts equally on the entire circular contour in the thin film, This also makes it difficult for cracks to occur.

  In addition, the gold electrode has a plurality of openings, each of the openings can accommodate a sample, and the lid and the substrate have observation windows formed at positions corresponding to the openings. Form may be sufficient.

  According to this embodiment, it is possible to simultaneously observe electrochemical changes of a plurality of samples with one electrochemical measurement cell.

  In addition to providing a plurality of openings in the gold electrode so that the plurality of samples are positioned at positions corresponding to the respective observation windows, the plurality of samples can be fixed at desired positions in the gold electrode. Since the sample is accommodated in the opening, the sample can be in contact with the gold electrode around it, which leads to promotion of the electrochemical change.

  The present invention also extends to an electrochemical measurement system. In this electrochemical measurement system, a holder for fixing the electrochemical measurement cell is a transmission electron microscope (aberration-corrected transmission electron microscope (Cs-TEM)). Is included).

  In this electrochemical measurement system, since the electrochemical measurement cell according to the present invention is set in the transmission electron microscope in a state of being fixed to the holder, both electrochemical measurement and sample observation can be achieved. In addition, by applying the electrochemical measurement cell according to the present invention, it is possible to transmit an electron beam through an electron beam transmission thin film having a nano-size thickness, thereby improving the resolution.

  As can be understood from the above description, according to the electrochemical measurement cell of the present invention and the electrochemical measurement system in which this cell is set in a transmission electron microscope, it is possible to achieve both electrochemical measurement and sample observation. For example, electrochemical changes of an electrode catalyst for a fuel cell such as a Pt catalyst can be observed in real time.

It is a longitudinal cross-sectional view of embodiment of the cell for electrochemical measurements of this invention. It is an II-II arrow line view of FIG. It is the III-III arrow line view of FIG.

  Embodiments of the electrochemical measurement cell of the present invention will be described below with reference to the drawings. The illustrated example is a pair of electrode pairs, but may be a form having two or more electrode pairs or a form having three or more electrodes.

(Electrochemical measurement cell)
FIG. 1 is a longitudinal sectional view of an embodiment of an electrochemical measurement cell according to the present invention, and FIG. 2 is a plan view of the electrochemical measurement cell as viewed from above, taken along the line II-II in FIG. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 1 and the electrochemical measurement cell cut along the way.

  In the illustrated electrochemical measurement cell 10, an electrode pair composed of a gold electrode 5 and a platinum electrode 4 is formed on a substrate 3 composed of an electron beam permeable thin film 1 and a stiffening plate 2. A space 6 on the thin film 1 surrounded by the surrounding frame 6 is filled with the electrolyte solution ES so as to seal the electrode pair, and an electron beam is transmitted above the surrounding frame 6. A lid 9 consisting of a conductive thin film 7 and a stiffening plate 8 is disposed to constitute the whole.

  Each of the thin films 1 and 7 constituting the substrate 3 and the lid 9 is an extremely thin film having a thickness of about 10 nm to 20 nm, and is formed of any one of silicon nitride, silicon dioxide, amorphous silicon, and the like. ing.

  Further, the stiffening plates 2 and 8 constituting the substrate 3 and the lid 9 are for forming the substrate 3 and the lid 9 having a desired rigidity by imparting rigidity to the thin films 1 and 7, respectively. It is made of silicon (silicon) or the like.

  The planar dimension of the electrochemical measurement cell 10 is about several mm square, and the enclosure frame 6 is made of ceramics such as silicon dioxide from the viewpoint of preventing the electrode pair from being short-circuited in such an extremely small cell.

As apparent from FIG. 3, the inner frame 6 a of the surrounding frame 6 is composed of four planes and a continuous surface of four curved surfaces 6 a ′ connecting them. In a state where the enclosure solution 6 made of silicon dioxide or the like is filled with the electrolyte solution ES, the periphery of the electrolyte solution ES is generally hydrophobic, and there is a corner portion on the inner surface of the enclosure frame. Therefore, gas accumulation can be eliminated by making the inner surface 6a of the surrounding frame 6 a continuous surface of a flat surface and a curved surface as shown in the example of the drawing.
In addition, any one of perchloric acid, sulfuric acid, and nitric acid is used as the electrolytic solution ES.

  The gold electrode 5 is provided with a plurality of openings 5a (four openings in the figure), and a sample S to be observed (for example, a Pt catalyst for a fuel cell) is accommodated in the openings 5a. Yes. In addition, although the planar shape of the opening 5a shown in the figure is a rectangle (see FIG. 3), the planar view shape may be a polygon other than a rectangle, a circle, an ellipse, or the like. Furthermore, an opening having a shape complementary to the sample to be accommodated may be provided so that the sample can be accommodated in the opening in a stationary posture.

  As described above, when the sample S to be observed is in contact with the gold electrode 5, the gold electrode 5 is electrically stable, and measurement noise can be reduced. In particular, when Pt or an alloy thereof frequently used as an electrode catalyst for a fuel cell is used as the sample S, the gold electrode is suitable for contacting the gold electrode 5 and observing the change (platinum electrode). When a platinum catalyst is brought into contact with the catalyst, an electrochemical reaction of only the platinum catalyst cannot be observed). In addition, since the plurality of samples S are accommodated in the plurality of openings 5 a provided in the gold electrode 5, the plurality of samples S can be fixed at desired positions in the gold electrode 5, and the sample S is inserted in the opening 5 a. Is accommodated, the sample S can contact the gold electrode 5 around it, and the electrochemical change can be promoted.

  Further, the stiffening plates 2 and 8 constituting the substrate 3 and the lid 9 are provided with observation windows 2a and 8a through which the sample S in each opening 5a of the gold electrode 5 can be confirmed at a position corresponding to each opening 5a. Therefore, each of the four observation windows 2a and 8a is opened at a position corresponding to each other.

  Therefore, as shown in FIG. 2, the opening 5a of the gold electrode 5 positioned below and the sample S in contact therewith can be confirmed through the observation window 8a.

  Further, the electron beam EB can be transmitted through the corresponding observation windows 2a and 8a when observing with a transmission electron microscope.

  Further, as apparent from FIG. 2, the planar shape of the observation window 8a is circular. Since the inside of the transmission electron microscope is an ultra-high vacuum atmosphere, while the inside of the cell 10 is an atmospheric pressure atmosphere, the structure of the observation window 8a (and the observation window 2a) that can withstand this pressure difference is required. Since the planar shape of the observation windows 8a and 2a is circular, the tensile force due to the pressure difference between the inside and outside of the cell acts on the thin film 7 and 1 evenly over the entire circular contour, which also causes cracks. Is less likely to occur.

  According to the illustrated electrochemical measurement cell 10, it is possible to achieve both electrochemical measurement and sample observation. For example, it is possible to observe in real time an electrochemical change of an electrode catalyst for a fuel cell such as a Pt catalyst. Become. In addition, even though the cell is small in size, electrical insulation is guaranteed, and the possibility of damage to the observation window is extremely low even in an ultrahigh vacuum atmosphere during TEM observation. Furthermore, since the sample can be imaged through a nano-sized ultra-thin film, the resolution is extremely high.

  Such an electrochemical measurement cell 10 is fixed to a holder (not shown) and set in a transmission electron microscope (not shown) to constitute an electrochemical measurement system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Thin film, 2 ... Stiffening plate, 2a ... Observation window, 3 ... Substrate, 4 ... Platinum electrode, 5 ... Gold electrode, 5a ... Opening, 6 ... Enclosure frame, 6a ... Inner side surface, 6a '... Curved surface, 7 ... Thin film, 8 ... Stiffening plate, 9 ... Lid, 10 ... Electrochemical measurement cell, ES ... Electrolyte, S ... Sample, EB ... Electron beam

Claims (5)

An electrochemical measurement cell,
A substrate made of an electron beam permeable thin film and a stiffening plate, an electrode pair made of a gold electrode and a platinum electrode placed on the thin film of the substrate, an enclosure frame surrounding the electrode pair on the thin film, and an enclosure frame An electrolyte solution that seals the electrode pair in the space surrounded by the thin film, and a lid that is disposed above the enclosure frame and is made of an electron beam permeable thin film and a stiffening plate.
Both the lid and the stiffening plate of the substrate are cut out at positions corresponding to the gold electrodes to form an observation window, and a sample in contact with the gold electrode can be confirmed from the observation window. Electrochemical measurement cell that allows the electron beam to pass through the sample in between.   2. The electrochemical measurement cell according to claim 1, wherein, of the enclosure frame, an inner surface facing the electrode pair is formed of a curved surface or a surface in which a flat surface and a curved surface are continuous.   The electrochemical measurement cell according to claim 1 or 2, wherein the planar shape of the observation window is circular.   The gold electrode has a plurality of openings, the sample can be accommodated in each of the openings, and an observation window is formed at a position corresponding to each of the openings in the lid and the substrate. 4. The electrochemical measurement cell according to any one of 3.   An electrochemical measurement system in which a holder for fixing the electrochemical measurement cell according to claim 1 is set on a transmission electron microscope.

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