Electrochemical cell

Abstract

To provide an electrochemical cell capable of obtaining a measurement result less affected by bubbles even when a current density supplied to the electrochemical cell is increased in operando measurement, for example, obtaining a measurement result suitable for industrial use.SOLUTION: An electrochemical cell of the present invention includes: an anode member having a water supply part and a water / oxygen discharge part; a cathode member transmitting X-rays; and a cover member provided on a side opposite to a side on which the anode member is provided with respect to the cathode member. The cover member has an opening that allows X-rays to pass from a side opposite to the side on which the anode member and the cathode member are provided during operando measurement.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to electrochemical cells. [Background technology]

[0002] Demand for hydrogen storage systems that store renewable energy as hydrogen fuel is increasing. Hydrogen storage systems use surplus electricity to electrolyze water in a water electrolysis cell, storing energy in the form of hydrogen, and in times of power shortage, use the stored hydrogen to generate electricity in a fuel cell to make up for the power shortage. Technology related to electrochemical cells that function as water electrolysis cells and fuel cell cells is disclosed, for example, in Patent Document 1.

[0003] X-ray absorption spectroscopy (XAS) using radiation is used to obtain knowledge for the development of catalysts used in electrochemical cells. In particular, measurement of the state of the catalyst during the operation of the electrochemical cell (operando measurement) is important. For example, operando measurement can provide knowledge about the structure and electronic state of the catalyst during the electrochemical reaction in the electrochemical cell. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-066799 Summary of the Invention [Problem to be solved by the invention]

[0005] Bubbles generated during water electrolysis cause fluctuations in X-ray absorbance and affect the results of operando measurements. The higher the current density supplied to the electrochemical cell, the more bubbles are generated. For this reason, conventionally, the current density was set to approximately 10 mAcm. -2 Operand measurements were performed with the following restrictions:

[0006] However, for industrial applications, efficient hydrogen production requires approximately 10 mAcm-2 Hundreds to thousands of mAcm, about two orders of magnitude larger than -2 Therefore, conventional operando measurements cannot provide measurement results suitable for industrial applications.

[0007] Therefore, an object of the present invention is to provide an electrochemical cell that can obtain measurement results in operando measurements that are less affected by bubbles even when the current density supplied to the electrochemical cell is increased, for example, that can obtain measurement results suitable for industrial applications. [Means for solving the problem]

[0008] The electrochemical cell of the present invention includes an anode member having a water supply section and a water and oxygen discharge section, a cathode member that is transparent to X-rays, and a cover member that is provided on the side of the cathode member opposite to the side on which the anode member is provided, the cover member having an opening that allows X-rays to pass through from the side opposite to the sides on which the anode member and the cathode member are provided during operando measurement. The anode member is a member on the anode electrode side, and the cathode member is a member on the cathode electrode side. The anode member may be interpreted as an anode current collector, and the cathode member may be interpreted as a cathode current collector.

[0009] Between the anode member and the cathode member, a structure is provided in which an electrolyte membrane is sandwiched between an anode catalyst and a cathode catalyst. The anode catalyst is a catalyst on the anode electrode side, and the cathode catalyst is a catalyst on the cathode electrode side. This structure is the object of operand measurement, and It may be detachable from the chemical cell and may be modified as appropriate.

[0010] In both conventional electrochemical cells and the electrochemical cell of the present invention, bubbles are generated on the outer surface (anode electrode side) of the anode catalyst. When attempting to perform surface analysis of the anode catalyst using operando measurement, conventional operando measurement, particularly transmission measurement, irradiates the anode catalyst with X-rays from the anode electrode side, causing the X-rays to pass through the bubbles generated on the outer surface of the anode catalyst. As a result, the results of the operando measurement are significantly affected by the bubbles generated on the outer surface of the anode catalyst. In the operando measurement of the present invention, X-rays are irradiated onto the anode catalyst from the cathode electrode side (the opening in the cover member) and fluorescent X-rays emitted to the outside through the opening in the cover member are detected, thereby preventing the X-rays from passing through the bubbles generated on the outer surface of the anode catalyst. As a result, measurement results can be obtained that are not affected by the bubbles generated on the outer surface of the anode catalyst. A similar effect can be obtained even when the current density supplied to the electrochemical cell is increased, making it possible to obtain measurement results suitable for industrial applications.

[0011] The electrolyte membrane may be a solid polymer electrolyte membrane, which allows water to be supplied only from the anode catalyst side, thereby preventing bubbles from forming on the surface of the cathode catalyst and more reliably obtaining measurement results that are not affected by bubbles.

[0012] The structure may further include an anode catalyst support member that supports the anode catalyst from the anode member side and a cathode catalyst support member that supports the cathode catalyst from the cathode member side. In this case, the anode catalyst support member may be interpreted as an anode current collector, or the combination of the anode member and the anode catalyst support member may be interpreted as an anode current collector. Similarly, the cathode catalyst support member may be interpreted as a cathode current collector, or the combination of the cathode member and the cathode catalyst support member may be interpreted as a cathode current collector. When the structure is fabricated independently, it is easy to ensure good contact between the anode catalyst and the anode catalyst support member, and good contact between the cathode catalyst and the cathode catalyst support member. Therefore, by including an anode catalyst support member and a cathode catalyst support member in the structure, good contact between the anode catalyst and the anode current collector and between the cathode catalyst and the cathode current collector can be achieved. The anode member, the anode catalyst support member, and the anode catalyst may each be interpreted as at least a part of an anode electrode, and the cathode member, the cathode catalyst support member, and the cathode catalyst may each be interpreted as at least a part of a cathode electrode.

[0013] The anode catalyst support member may be a mesh member, which allows the anode catalyst support member to function as a gas diffusion layer, diffusing bubbles generated on the outer surface of the anode catalyst, thereby more reliably obtaining measurement results that are not affected by the bubbles.

[0014] The device may further include a heater provided on the anode member side. The use of the heater can promote the electrolysis of water and enable operando measurements at temperatures suitable for industrial applications. The heater is provided on the anode member side so as not to obstruct the optical path of the X-rays.

[0015] The present invention may be considered to be a measurement method characterized by comprising the steps of irradiating a structure in which an electrolyte membrane is sandwiched between an anode catalyst and a cathode catalyst, the structure being provided between the anode member and the cathode member in the electrochemical cell, with X-rays from the opening, and detecting fluorescent X-rays emerging from the opening. [Effects of the Invention]

[0016] According to the present invention, in operando measurement, it is possible to obtain measurement results that are less affected by bubbles even when the current density applied to the electrochemical cell is increased, for example, to obtain measurement results suitable for industrial applications. It is possible to provide an electrochemical cell that enables [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1(A) is a schematic diagram showing the configuration of an electrochemical cell according to this embodiment, and FIG. 1(B) is a schematic diagram showing the configuration of a structure (subject of operand measurement) according to this embodiment. [Figure 2] FIG. 2(A) is a schematic diagram showing how water electrolysis is performed in operando measurement according to this embodiment and how X-rays are irradiated onto the anode catalyst, and FIG. 2(B) is a graph showing the measurement results according to this embodiment (the results of operando measurement on the anode catalyst). [Figure 3] FIG. 3 is a schematic diagram showing how water is electrolyzed and how X-rays are irradiated onto the cathode catalyst in operando measurement according to this embodiment. [Figure 4] FIG. 4(A) is a schematic diagram showing the configuration of a conventional electrochemical cell, and FIGS. 4(B) and 4(C) are graphs showing the results of conventional measurements (results of operando measurements on an anode catalyst). DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] First, problems that arise in conventional electrochemical cells will be described. The inventors fabricated a conventional electrochemical cell and performed operando measurements (X-ray absorption measurements) on the beamline BL14B2 of the large synchrotron radiation facility, SPring-8.

[0020] FIG. 4(A) is a schematic diagram showing the configuration of a conventional electrochemical cell 400. In the electrochemical cell 400, an anode catalyst 402 and a cathode catalyst 403 are inserted into an electrolyte 401 containing 1M H2SO4. A commercially available iridium catalyst (iridium loading: 0.2 mg) was used as the anode catalyst 402. Ir cm -2 The electrochemical cell 400 is made of IrO2 (Elyst Ir75 0480 manufactured by Umicore). A Kapton film (0.2 mm thick) is provided as an X-ray irradiation window 404 on the side of the electrochemical cell 400 (the anode catalyst 402 side). The distance from the anode catalyst 402 to the X-ray irradiation window 404 is 0.5 mm.

[0021] Operando X-ray absorption measurements of the iridium L3 absorption edge were performed using the fluorescence method. Figures 4(B) and 4(C) are graphs showing the results of operando measurements. Figure 4(B) is a graph showing the X-ray absorption spectrum, and Figure 4(C) is a graph showing the normalized X-ray absorption spectrum.

[0022] The X-ray absorption spectrum shown in Figure 4(B) is obtained at 1 mAcm -2 The X-ray absorption near-edge structure (XANES) spectrum was obtained during water electrolysis by supplying a current to the electrochemical cell at a low current density of 10 mAcm. As indicated by the arrows in Figure 4(B), several sudden changes in absorbance were observed in the post-edge region. -2 When the temperature was increased to 400°C, the abrupt changes in absorbance became more pronounced. These abrupt changes are thought to be due to oxygen bubbles generated on the surface of the anode catalyst 402. These abrupt changes make extended X-ray absorption fine structure (EXAFS) spectrum analysis impossible. Furthermore, as shown in Figure 4(C), these abrupt changes affect normalization, reducing the reliability of the XANES spectrum analysis results.

[0023] This embodiment solves this problem. Specifically, in operando measurement, it is possible to obtain measurement results that are less affected by bubbles even when the current density supplied to the electrochemical cell is increased, for example, to obtain measurement results suitable for industrial applications.

[0024] 1(A) is a schematic diagram (exploded perspective view) showing the configuration of an electrochemical cell 100 according to this embodiment. The electrochemical cell 100 has an anode member 101, a cathode member 102, and a cover member 103. The anode member 101 is a member on the anode electrode side, and the cathode member 102 is a member on the cathode electrode side.

[0025] The anode member 101 is formed with a water supply portion 101in, a water discharge portion 101out1, and an oxygen discharge portion 101out2. The water discharge portion and the oxygen discharge portion may be a common portion. The anode member 101 is made of a conductor, and in this embodiment is made of titanium. The thickness of the anode member 101 in the stacking direction of the anode member 101, the cathode member 102, and the cover member 103 is 10 mm. An anode cable is connected to the anode member 101.

[0026] When performing surface analysis of an anode catalyst using operando measurement, conventional operando measurement irradiates the anode catalyst with X-rays from the anode electrode side, but in operando measurement according to this embodiment, X-rays are irradiated onto the anode catalyst from the cathode electrode side. Therefore, the cathode member 102 is made of a conductor that transmits X-rays, and in this embodiment, it is made of carbon. Specifically, a commercially available carbon plate (manufactured by Nilaco Japan, thickness 0.2 mm to 0.5 mm) is used as the cathode member 102. A cathode cable is connected to the cathode member 102.

[0027] The cover member 103 is provided on the side of the cathode member 102 opposite to the side on which the anode member 101 is provided. The material of the cover member 103 is not particularly limited, but it is preferable that the cover member 103 be optically transparent, and in this embodiment, it is made of PTFE (polytetrafluoroethylene). The cover member 103 has an opening 103o that allows X-rays to pass through from the side opposite to the side on which the anode member 101 and the cathode member 102 are provided during operando measurement.

[0028] A structure 104 is provided between the anode member 101 and the cathode member 102. Fig. 1(B) is a schematic diagram showing the configuration of the structure 104. The structure 104 has an anode catalyst 104a, a cathode catalyst 104b, and an electrolyte membrane 104c sandwiched between the anode catalyst 104a and the cathode catalyst 104b.

[0029] The anode catalyst 104a is a catalyst on the anode electrode side. In this embodiment, a commercially available iridium catalyst (with an iridium loading of 0.2 mg) is used as the anode catalyst. Ir cm -2 The cathode catalyst 104b is a catalyst on the cathode electrode side, and in this embodiment, a ruthenium catalyst is used as the cathode catalyst 104b. A platinum catalyst may also be used as the cathode catalyst 104b. A known ion exchange membrane used in water electrolysis may be used as the electrolyte membrane 104c. The structure 104 is the subject of operando measurement, and may be detachable from the electrochemical cell 100 and may be modified as appropriate.

[0030] In both conventional electrochemical cells and the electrochemical cell 100 according to this embodiment, bubbles are generated on the outer (anode electrode side) surface of the anode catalyst. As described above, when performing surface analysis of the anode catalyst using operando measurement, conventional operando measurement irradiates the anode catalyst with X-rays from the anode electrode side, and therefore, in both transmission and fluorescence methods, the X-rays pass through the bubble portion generated on the outer surface of the anode catalyst. As a result, the results of operando measurement are significantly affected by the bubble portion generated on the outer surface of the anode catalyst. In operando measurement according to this embodiment, X-rays are irradiated onto the anode catalyst 104a from the cathode electrode side (opening 103o of cover member 103) and fluorescent X-rays emitted to the outside from opening 103o of cover member 103 are detected, thereby preventing the X-rays from passing through the bubble portion generated on the outer surface of the anode catalyst 104a. As a result, measurement results can be obtained that are not affected by bubbles generated on the outer surface of the anode catalyst 104a. The same effect can be obtained when the current density supplied to the electrochemical cell 100 is increased, making it possible to obtain measurement results suitable for industrial applications.

[0031] The electrolyte membrane 104c may be a solid polymer electrolyte membrane made of a perfluorocarbon resin or the like to which ion-exchange groups have been introduced, and this is the case in this embodiment. Specifically, Nafion 115 with a thickness of 0.17 mm is used as the electrolyte membrane 104c. This allows water to be supplied only from the anode catalyst 104a side, eliminating the generation of bubbles on the surface of the cathode catalyst 104b and ensuring measurement results that are not affected by bubbles.

[0032] Furthermore, in this embodiment, the structure 104 also has an anode catalyst support member 104d and a cathode catalyst support member 104e.

[0033] The anode catalyst support member 104d is a member that supports the anode catalyst 104a from the anode member 101 side, and is made of a conductor like the anode member 101. The anode catalyst support member 104d may be a mesh member, and in this embodiment, a titanium mesh is used as the anode catalyst support member 104d. In this way, the anode catalyst support member 104d functions as a gas diffusion layer, diffusing bubbles generated on the outer surface of the anode catalyst 104a, and making it possible to more reliably obtain measurement results that are not affected by the bubbles.

[0034] The cathode catalyst support member 104e is a member that supports the cathode catalyst 104b from the side of the cathode member 102, and is made of a conductor that transmits X-rays, similar to the cathode member 102. In this embodiment, the cathode catalyst 104b and the cathode catalyst support member 104e are combined using a commercially available Ru / C (a structure in which 5 wt % ruthenium is provided on carbon black, manufactured by Sigma Aldrich, with a ruthenium support amount of 0.2 mg). Ru cm -2 ) is used. As a combination of the cathode catalyst 104b and the cathode catalyst support member 104e, a commercially available Pt / C (a structure in which 20 wt% of platinum is provided on carbon black, Fuel Cell Earth Co., Ltd., platinum loading 0.2 mg Pt cm -2 ) may also be used.

[0035] When the structure 104 is produced independently, it is easy to bring the anode catalyst support member 104d into good contact with the anode catalyst 104a, and the cathode catalyst support member 104e into good contact with the cathode catalyst 104b. Therefore, by including the anode catalyst support member 104d and the cathode catalyst support member 104e in the structure 104, good contact between the anode catalyst 104a and the anode current collector, and good contact between the cathode catalyst 104b and the cathode current collector can be achieved.

[0036] The anode member 101 may be interpreted as an anode current collector, the anode catalyst support member 104d may be interpreted as an anode current collector, or the combination of the anode member 101 and the anode catalyst support member 104d may be interpreted as an anode current collector. Similarly, the cathode member 102 may be interpreted as a cathode current collector, the cathode catalyst support member 104e may be interpreted as a cathode current collector, or the combination of the cathode member 102 and the cathode catalyst support member 104e may be interpreted as a cathode current collector. The anode member 101, the anode catalyst support member 104d, and the anode catalyst 104a may each be interpreted as at least a part of an anode electrode. Similarly, the cathode member 102, the cathode catalyst support member 104e, and the cathode catalyst 104b may each be interpreted as at least a part of a cathode electrode.

[0037] Furthermore, in this embodiment, the electrochemical cell 100 has a heater 105. The heater 105 is provided on the anode member 101 side so that the heater 105 does not obstruct the optical path of the X-rays. In this embodiment, a PTC heater is used as the heater 105. The heater 105 can be used to accelerate the electrolysis of water and to enable operando measurements at temperatures suitable for industrial applications.

[0038] As shown in FIG. 1(A), the electrochemical cell 100 is completed by stacking a heater 105, an anode member 101, a structure 104, a cathode member 102, and a cover member 103 and fixing them with four sets of bolts and nuts.

[0039] The inventors prepared the electrochemical cell 100 described above, and performed operando high-energy resolution XANES measurements at the beamline BL36XU of the large synchrotron radiation facility SPring-8, by raising the temperature of the electrochemical cell 100 to 80° C. using a heater 105.

[0040] 2(A) is a schematic diagram showing how water electrolysis occurs in the electrochemical cell 100. As shown in FIG. 2(A), a water oxidation reaction occurs on the anode catalyst 104a side, producing oxygen and protons. These protons pass through the electrolyte membrane 104c to reach the cathode catalyst 104b, where they combine to form hydrogen gas rather than hydrogen bubbles.

[0041] First, the inventors performed operando measurements on the anode catalyst 104a (specifically, the iridium L3 absorption edge). As shown in Fig. 2(A), X-rays penetrated the cathode member 102, the cathode catalyst support member 104e, the cathode catalyst 104b, and the electrolyte membrane 104c in that order, before reaching the anode catalyst 104a.

[0042] 2B is a graph showing the results of operando measurement (X-ray absorption spectrum) of the anode catalyst 104a. -2 A high-energy resolution XANES spectrum was measured during water electrolysis by supplying a current to the electrochemical cell at a current density of 104a. A sharper white line than that observed in conventional XANES (Figure 4(B)) was observed. Furthermore, despite the extremely high current density, no sudden change in absorbance was observed in the post-edge region. This result proves that the X-ray absorption spectrum is not affected by oxygen bubbles generated on the outer surface of the anode catalyst 104a.

[0043] Furthermore, six cycles of operando measurement were performed over a one-hour period, but no change was observed in the X-ray absorption spectrum. This result proves that the anode catalyst 104a did not shift during the operando measurement and was continuously maintained at the desired position.

[0044] These two results demonstrated that reliable analysis of XANES spectra is possible.

[0045] Note that operando measurement targeting the cathode catalyst 104b (e.g., the ruthenium K absorption edge) can also provide highly reliable measurement results, similar to operando measurement targeting the anode catalyst 104a. When the cathode catalyst 104b is the target, as shown in Fig. 3, X-rays pass through (the cathode member 102 and) the cathode catalyst support member 104e and are irradiated onto the cathode catalyst 104b.

[0046] As described above, according to this embodiment, in operando measurement, it is possible to obtain measurement results that are less affected by bubbles even when the current density supplied to the electrochemical cell is increased, and for example, it is possible to obtain measurement results that are suitable for industrial applications. -2 Even at high current densities and temperatures as high as 80°C, highly reliable measurement results can be obtained.

[0047] It should be noted that the above-described embodiment is merely an example, and the present invention also includes modifications and variations of the above-described embodiment that are obtained within the scope of the gist of the present invention. The invention is applicable to both operando measurements of anode catalysts and operando measurements of cathode catalysts. [Explanation of symbols]

[0048] 100: Electrochemical cell 101: Anode member 101in: Supply section 101out1: Discharge section 101out2: Discharge section 102: Cathode member 103: Cover member 104: Structure 104a: Anode catalyst 104b: Cathode catalyst 104c: Electrolyte membrane 104d: Anode catalyst support member 104e: Cathode catalyst support member 105: Heater 400: Electrochemical cell 401: Electrolyte 402: Anode catalyst 403: Cathode catalyst 404: X-ray irradiation window

Claims

1. an anode member having a water supply and a water and oxygen exhaust; a cathode member that transmits X-rays; a cover member provided on the side of the cathode member opposite to the side on which the anode member is provided; and The cover member has an opening through which X-rays pass from the side opposite to the side on which the anode member and the cathode member are provided during operand measurement. Electrochemical cell characterized by:

2. Between the anode member and the cathode member, a structure in which an electrolyte membrane is sandwiched between an anode catalyst and a cathode catalyst is provided.

2. The electrochemical cell of claim 1.

3. The electrolyte membrane is a solid polymer electrolyte membrane.

3. The electrochemical cell of claim 2.

4. The structure further includes an anode catalyst support member that supports the anode catalyst from the anode member side, and a cathode catalyst support member that supports the cathode catalyst from the cathode member side.

4. The electrochemical cell according to claim 2 or 3.

5. The anode catalyst support member is a mesh member.

5. The electrochemical cell of claim 4.

6. The anode member further includes a heater provided on the anode member side.

4. The electrochemical cell according to claim 1, wherein the electrochemical cell is a polyimide.

7. a step of irradiating a structure in which an electrolyte membrane is sandwiched between an anode catalyst and a cathode catalyst, the structure being provided between the anode member and the cathode member in the electrochemical cell according to claim 1, with X-rays through the opening; detecting fluorescent X-rays emerging from the opening; A measuring method comprising:

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