Cu POROUS MEMBER

Abstract

To provide a Cu porous member of sufficient strength and a small pressure loss to gas or liquid, capable of accelerating CO2 reductive reaction to efficiently produce an organic compound with 2C or higher, such as ethanol.SOLUTION: The Cu porous member comprises: a member body 11 constituted of Cu or a Cu alloy to form a porous structure; and a nano Cu structure layer 16 formed at least on a part of a surface of the member body 11, wherein a porosity of the member body 11 is in a range of 38% or more and 95% or less, and a thickness is in a range of 0.1 mm or more and 1.0 mm or less, and the nano Cu structure layer 16 is constituted as a layer by overlaying Cu particles of a mean length of from 20 μm to 1 nm on a surface thereof.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a Cu porous member made of Cu or a Cu alloy, and particularly to a Cu porous member suitable as an electrode for carbon dioxide reduction by a co-electrolysis method.

Background Art

[0002] At present when global warming is accelerating, particularly the reduction of GHGs such as CO2 gas in the atmosphere is a common global issue. In recent years, the development of CCU (Carbon dioxide Capture, Utilization) technology that uses carbon dioxide in the atmosphere as a raw material for useful chemical products has been accelerating. Carbon dioxide has a maximum oxidation state with an oxidation number of +4 for carbon and is a very stable compound with a standard Gibbs free energy of about 400 kJ / mol. In order to convert carbon dioxide into useful chemical products, it is necessary to reduce carbon with a large amount of energy. The development of technology that can efficiently reduce carbon dioxide is required.

[0003] In recent years, the co-electrolysis method using an electrolytic cell composed of a polymeric ion exchange membrane has attracted attention (see, for example, Patent Documents 1 and 2). The co-electrolysis method is a technique in which electrolysis by an oxidation reaction is performed at the anode and electrolysis by a reduction reaction is performed at the cathode simultaneously in an electrochemical cell. For example, by using water at the anode and an aqueous solution of KHCO3 or CO2 gas at the cathode as raw materials, CO2 can be reduced using protons generated from the electrolysis of H2O. When Ag is used as a catalyst, CO gas can be obtained from CO2 with high Faraday efficiency.

[0004] When Cu is used as a catalyst, organic compounds having two or more carbon atoms (for example, ethanol, etc.) can be obtained from CO2 with high Faraday efficiency. In recent years, it has been clarified that the Faraday efficiency of compounds having two or more carbon atoms is improved due to differences in the oxidation number of Cu and the nano-scale geometric structure. By controlling the nano-structure, high-performance CO2 reduction catalysts have been proposed. Here, as the electrode for the co-electrolysis method, carbon paper supporting nano-sized Cu particles is used.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the case of carbon paper supporting nano-sized Cu particles, due to its weak mechanical strength, there is a risk of being crushed in the electrolytic cell. Also, when used as an electrode for the co-electrolysis method, it is necessary to introduce the raw material CO2 gas and discharge liquids such as ethanol generated after the reaction outside the cell. However, carbon paper has a relatively high pressure loss for gases and liquids, resulting in a problem of reduced production efficiency.

[0007] The present invention has been made against the background of the above circumstances, and an object thereof is to provide a Cu porous member having sufficient strength, low pressure loss for gases and liquids, and capable of promoting the CO2 reduction reaction to efficiently produce C2 or higher organic compounds such as ethanol.

Means for Solving the Problems

[0008] In order to solve such problems and achieve the above object, the Cu porous member of Aspect 1 of the present invention is composed of Cu or a Cu alloy, and includes a member body having a porous structure and a nano-Cu structure layer formed on at least a part of the surface of the member body. The member body has a porosity in the range of 38% or more and 95% or less, and a thickness in the range of 0.1 mm or more and 1.0 mm or less. The nano-Cu structure layer is characterized in that it is formed as a layer by laminating Cu particles having an average length of 20 μm to 1 nm on the surface.

[0009] According to the Cu porous member of Aspect 1 of the present invention, since it is composed of Cu or a Cu alloy and has a member body with a porous structure, and the porosity is in the range of 38% or more and 95% or less, and the thickness is in the range of 0.1 mm or more and 1.0 mm or less, the pressure loss of gas and liquid is reduced, and gas and liquid can flow stably. Also, the strength can be ensured, and it can be stably used as an electrode. And since a nano-Cu structure layer formed as a layer by laminating Cu particles having an average length of 20 μm to 1 nm on at least a part of the surface of the member body is formed, it becomes possible to efficiently reduce CO2 using the Cu particles having an average length of 20 μm to 1 nm as a catalyst and generate C2 or higher organic compounds such as ethanol.

[0010] The Cu porous member of Aspect 2 of the present invention is the Cu porous member of Aspect 1 of the present invention, wherein the nano-Cu structure layer is formed on one side of the member body, and the coverage rate of the nano-Cu structure layer on the one surface of the member body is 20% or more. According to the Cu porous member of Aspect 2 of the present invention, the catalytic action of Cu particles having an average length of 20 μm to 1 nm can be surely exerted, and it becomes possible to perform CO2 reduction more efficiently.

[0011] The Cu porous member of Embodiment 3 of the present invention is the Cu porous member of Embodiment 1 or Embodiment 2 of the present invention, wherein the Cu particles having an average length of 20 μm to 1 nm constituting the nano-Cu structure layer are in a dendrite shape or a spherical shape. According to the Cu porous member of Embodiment 3 of the present invention, since the Cu particles having an average length of 20 μm to 1 nm constituting the nano-Cu structure layer are in a dendrite shape or a spherical shape, the catalytic action of nano-Cu can be surely exerted, and CO2 reduction can be performed more efficiently.

[0012] The Cu porous member of Embodiment 4 of the present invention is the Cu porous member of any one of Embodiments 1 to 3 of the present invention, and is characterized in that the Faraday efficiency when ethanol is generated using it as an electrode in the co-electrolysis method is 1.0% or more. According to the Cu porous member of Embodiment 4 of the present invention, since the Faraday efficiency when ethanol is generated using it as an electrode in the electrolysis method is 1.0% or more, it is possible to efficiently generate ethanol by reducing CO2 by the co-electrolysis method.

Effects of the Invention

[0013] According to the present invention, it is possible to provide a Cu porous member having sufficient strength, low pressure loss against gases and liquids, and promoting the CO2 reduction reaction to efficiently generate C2 or higher organic compounds such as ethanol.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0015] Hereinafter, a Cu porous member which is an embodiment of the present invention will be described with reference to the attached drawings.

[0016] The Cu porous member 10 of the present embodiment is used, for example, as a cathode electrode in an electrolytic cell for performing electrolysis by an oxidation reaction at the anode and electrolysis by a reduction reaction at the cathode in a co-electrolysis method.

[0017] As shown in FIGS. 1 and 2, the Cu porous member 10 of the present embodiment includes a member main body 11 and a nano Cu structure layer 16 formed on at least a part of the surface of the member main body 11. In the present embodiment, as shown in FIGS. 1 and 2, the member main body 11 is a sheet material, and the nano Cu structure layer 16 is formed on one main surface (one surface) of the sheet material.

[0018] In the present embodiment, the member main body 11 made of Cu or a Cu alloy is a porous body as shown in FIG. 1, and includes a skeleton part 12 having a three-dimensional network structure and a pore part 13 surrounded by the skeleton part 12. Note that the pore parts 13 surrounded by the skeleton part 12 communicate with each other and have a structure that opens toward the outside of the member main body 11.

[0019] And the porosity P of this member main body 11 is in the range of 38% or more and 95% or less. By setting the porosity P of the member main body 11 to 38% or more, it becomes possible to allow gas and liquid to flow well. On the other hand, by setting the porosity P of the member main body 11 to 95% or less, the strength of the member main body 11 can be ensured and handling becomes easy. Incidentally, the porosity P of the member body 11 is preferably 45% or more, more preferably 50% or more. The porosity P of the member body 11 is preferably 93% or less, more preferably 90% or less.

[0020] Incidentally, the porosity P of the member body 11 is calculated by the following formula. P(%)=(1-(W / (V×D T )))×100 W: Mass of the member body 11 (g) V: Volume of the member body 11 (cm 3 ) D T : True density of the metal material constituting the member body 11 (g / cm 3 )

[0021] Also, the thickness of the member body 11 is in the range of 0.1 mm or more and 1.0 mm or less. Here, by setting the thickness of the porous-structured member body 11 to 0.1 mm or more, it becomes possible to sufficiently act as a flow path for gas or liquid. On the other hand, by setting the thickness of the member body 11 to 1.0 mm or less, it does not become excessively heavy and is easy to handle. Incidentally, the thickness of the member body 11 is preferably 0.2 mm or more, more preferably 0.3 mm or more. The thickness of the member body 11 is preferably 0.9 mm or less, more preferably 0.8 mm or less.

[0022] In this embodiment, the Cu or Cu alloy constituting the member body 11 made of a porous body preferably has a Cu content of 80% by mass or more, and may contain, for example, Zn, Sn, P, Ca, Be, Co, Ni, Fe, Mn, Al, Mg, etc. as elements other than Cu. By forming with a Cu or Cu alloy having a Cu content of 80% by mass or more, it becomes possible to ensure high conductivity. Incidentally, the Cu content in the Cu or Cu alloy constituting the member body 11 is preferably 85% by mass or more, more preferably 90% by mass or more.

[0023] And in the present embodiment, as shown in FIG. 3, the nano-Cu structure layer 16 is composed of Cu particles 18 having an average length of 20 μm to 1 nm. Here, in the present embodiment, the Cu particles 18 having an average length of 20 μm to 1 nm are preferably in a dendrite shape as shown in FIG. 3(a) or in a spherical shape as shown in FIG. 3(b).

[0024] Also, in the present embodiment, the average length of the Cu particles 18 having an average length of 20 μm to 1 nm that constitute the nano-Cu structure layer 16 is preferably in the range of 200 nm or more and 2000 nm or less. Note that the maximum average length L is the average length that can draw the longest straight line within the Cu particle 18 when observing the cross section of one Cu particle 18. By setting the average length of the Cu particles 18 to be in the range of 200 nm or more and 2000 nm or less, the Cu particles 18 having an average length of 20 μm to 1 nm can act efficiently as a catalyst and sufficiently promote the reduction reaction of CO2. In addition, the average length of the Cu particles 18 having an average length of 20 μm to 1 nm is more preferably 250 nm or more, and even more preferably 300 nm or more. Also, the average length of the Cu particles 18 having an average length of 20 μm to 1 nm is more preferably 1900 nm or less, and even more preferably 1800 nm or less.

[0025] Here, in the present embodiment, the coverage rate of the nano-Cu structure layer 16 on one surface of the member body 11 is preferably 20% or more. By setting the coverage rate of the nano-Cu structure layer 16 on one surface of the member body 11 to 20% or more, the Cu particles 18 having an average length of 20 μm to 1 nm become a catalyst layer and the reduction reaction of CO2 proceeds efficiently. In addition, the coverage rate of the nano-Cu structure layer 16 on one surface of the member body 11 is preferably 30% or more, and more preferably 40% or more.

[0026] In addition, in the present embodiment, it is preferable that the Faraday efficiency when ethanol is generated using it as an electrode of the co - electrolysis method is 1.0% or more.

[0027] The schematic diagram of the co - electrolysis apparatus using the Cu porous member 10 of the present embodiment is shown in FIG. 4 below. The co - electrolysis apparatus of the present embodiment is a solid polymer type co - electrolysis apparatus.

[0028] As shown in FIG. 4, the co - electrolysis apparatus 30 of the present embodiment includes an electrolytic cell 31 having an anode electrode 32 and a cathode electrode 33 arranged opposite to each other, an ion permeable membrane 34 arranged between the anode electrode 32 and the cathode electrode 33, and a catalyst layer 35. Here, for the anode electrode 32, the ion permeable membrane 34, and the catalyst layer 35, those used in a conventional general solid polymer type water electrolysis apparatus can be applied.

[0029] The above - mentioned cathode electrode 33 is composed of the Cu porous member 10 of the present embodiment, and includes a member main body 11 made of Cu or a Cu alloy, and a nano - Cu structure layer 16 formed on the surface of the member main body 11. Further, the member main body 11 is a porous body and has a structure including a skeleton portion 12 having a three - dimensional network structure and a pore portion 13 surrounded by the skeleton portion 12.

[0030] In the above - mentioned co - electrolysis apparatus 30 (electrolytic cell 31), as shown in FIG. 4, water (H2O) is supplied to the anode electrode 32 side, and CO2 is supplied to the cathode electrode 33 side. Then, an electric current is passed through the anode electrode 32 and the cathode electrode 33. Then, water is electrolyzed at the anode electrode 32, the generated oxygen (O2) is discharged from the anode electrode 32, and hydrogen (H2) moves to the cathode electrode 33. And at the cathode electrode 33, CO2 is reduced, and organic compounds having two or more carbon atoms such as ethanol are generated. The organic compounds having two or more carbon atoms such as the generated ethanol are discharged to the outside of the electrolytic cell 31 through the pore portion 13 of the member main body 11.

[0031] According to the Cu porous member 10 of the present embodiment configured as described above, it has a member body 11 having a porous structure made of Cu or a Cu alloy. Since the porosity P of this member body 11 is in the range of 38% or more and 95% or less, and the thickness is in the range of 0.1 mm or more and 1.0 mm or less, the pressure loss of gas and liquid is reduced, and gas and liquid can flow stably. Also, the strength can be ensured, and it can be stably used as an electrode. And since a nano-Cu structure layer 16 composed of Cu particles 18 having an average length of 20 μm to 1 nm is formed on at least a part of the surface of the member body 11, it is possible to efficiently reduce CO2 using nano-Cu as a catalyst and generate C2 or higher organic compounds such as ethanol.

[0032] In the present embodiment, when the nano-Cu structure layer 16 is formed on one surface of the member body 11 and the coverage rate of the nano-Cu structure layer 16 on one surface of the member body 11 is in the range of 20% or more and 100% or less, it is possible to sufficiently contact a raw material such as CO2 with Cu particles 18 having an average length of 20 μm to 1 nm serving as a catalyst, promote the CO2 reduction reaction, and more efficiently generate C2 or higher organic compounds such as ethanol.

[0033] In the present embodiment, when the Cu particles 18 having an average length of 20 μm to 1 nm constituting the nano-Cu structure layer 16 are in a dendrite shape or a spherical shape, the catalytic action of nano-Cu can be surely achieved, the CO2 reduction reaction can be promoted, and C2 or higher organic compounds such as ethanol can be more efficiently generated.

[0034] In this embodiment, when the average length of the Cu particles 18 having an average length of 20 μm to 1 nm that constitute the nano Cu structure layer 16 is in the range of 200 nm or more and 2000 nm or less, the raw materials such as CO2 and the Cu particles 18 having an average length of 20 μm to 1 nm serving as a catalyst can be sufficiently brought into contact with each other, and the CO2 reduction reaction can be promoted to more efficiently produce organic compounds having two or more carbon atoms such as ethanol.

[0035] In this embodiment, when the Faraday efficiency when producing ethanol using it as an electrode of the co-electrolysis method is 1.0% or more, it becomes possible to efficiently produce ethanol by reducing CO2 by the co-electrolysis method.

[0036] As described above, the embodiments of the present invention have been described. However, the present invention is not limited thereto, and can be appropriately changed without departing from the technical idea of the invention.

Example

[0037] Hereinafter, the results of the confirmation experiments conducted to confirm the effects of the present invention will be described. First, a member body shown in Table 1 is prepared. The dimensions of each prepared member body were 10 mm in width × 10 mm in length, and the thickness was as shown in Table 1. As shown in Table 1, a nano Cu structure layer was formed on one surface of this member body. In the comparative example, the nano Cu structure layer was not formed.

[0038] Here, the nano Cu structure layer composed of spherical Cu particles having an average length of 20 μm to 1 nm was produced as follows. A beaker with a diameter of 10 cm was filled with a 0.05 mol / L aqueous solution of copper pyrophosphate to prepare an electrodeposition solution. The member body was used as the working electrode, and a Pt mesh with a size of 25 mm × 10 mm was prepared as the counter electrode, and it was placed in the above beaker so that the distance between the working electrode and the counter electrode was 20 mm. Using a potentiostat (SP-50 manufactured by Bio-Logic), under the condition that the current density is 2 to 30 mA / cm 2 and the charge amount per electrode area is 2 C / cm 2Electroplating was performed so as to achieve this.

[0039] In addition, a nano-Cu structure layer composed of Cu particles with a dendritic shape and an average length of 20 μm to 1 nm was fabricated as follows. A 0.05 mol / L aqueous solution of copper pyrophosphate was filled in a beaker with a diameter of 10 cm to prepare an electroplating solution. The main body of the member was used as the working electrode, and a Pt mesh with a size of 25 mm × 10 mm was prepared as the counter electrode. The working electrode - counter electrode distance was set to 20 mm and installed in the above beaker. Using a potentiostat (SP-50 manufactured by Bio-Logic), the current density was 50 mA / cm 2 Under the above conditions, electroplating was performed so that the charge amount per electrode area was 2 C / cm 2 Electroplating was performed so as to achieve this.

[0040] The sample with the nano-Cu structure layer formed as described above was taken out, and the surface structure was observed using a desktop SEM (JCM-7000 manufactured by JEOL Ltd.). The acceleration voltage was 15 kV, and the measurement magnification was 5000 times when observing spherical nano-sized Cu particles and 10000 times when measuring dendritic nano-sized Cu particles. SEM images were taken, and the film thickness was measured using the measurement mode of the device. The obtained images were analyzed using analysis software (Fuji ImageJ). First, the image quality was adjusted with a Gaussian Blur 3D filter with Xsigma, Ysigma, and Zsigma each set to 2.0. Then, the binarization process was performed in the following procedure. A graph with intensity on the vertical axis and light and dark on the horizontal axis was created from the Image → Adjust → Threshold item. Based on the light and dark position of the peak observed in the obtained spectrum (when multiple peaks occur, the peak at the position with the highest brightness was used), the light and dark were separated to perform the binarization process. Subsequently, the boundaries of the particles were separated from the obtained binary image by the Watershed algorithm. Then, the Analyze Particles process (with the set values: size; 0 - Infinity, Circularity; 0.00 - 1.00) was performed to calculate the shape, average length, and coverage rate of the nano-sized Cu particles. For the determination of the particle shape, the values of Major (major axis) and Minor (minor axis), the parameters defining the ellipticity, in the summary file obtained after the analysis of Analyze Particles were used. When the value of Major / Minor exceeded 1.7, it was defined as a dendrite shape, and when it was 1.7 or less, it was defined as a particle shape. For the calculation of the average length, the value of Average Size (A) in the summary file obtained after the analysis of Analyze Particles was used, and the average length was calculated and determined using the formula: average length = 2 × √(A / π). Regarding the coverage rate, the value of %Area in the summary file obtained after the analysis of Analyze Particles was used.

[0041] The thickness of the member body was measured with a micrometer (Mitutoyo).

[0042] The porosity of the member body was calculated from the mass and volume of the member body using the following formula. P(%)=(1-(W / (V×D T )))×100 W: Mass (g) of the member body 11 V: Volume (cm 3 ) D T : True density (g / cm 3 ) of the metal material constituting the member body 11

[0043] The obtained Cu porous member was incorporated into an electrolytic cell as the cathode electrode, and the Faradaic efficiency was measured when ethanol was produced from CO2 by electrolysis. The evaluation results are shown in Table 1.

[0044] An example obtained at the cathode of an electrochemical cell of the 1 cm 2 level incorporating an anion exchange type ion exchange membrane, the current density being measured with a potentiostat (BioLogic HCP-803) at 100 mA / cm 2 and controlled to flow between the electrodes. At the anode, pure water as a raw material was flowed at 10 cc / min using a precision diaphragm pump (Tacmina Smooth Flow Pump Q series). At the cathode, pure CO2 gas was controlled to 10 cc / min with a mass flow controller (manufactured by KOFLOC), and further, a 0.1 M aqueous KHCO3 solution was controlled to 1 cc / min with a precision diaphragm pump (FLOM; KP21) and flowed.

[0045] The solution after the reaction discharged from the cathode was separated from the gas, and the ethanol concentration contained in the obtained liquid was measured with a high performance liquid chromatograph (JASCO Extrema). Taking the ethanol concentration obtained with the high performance liquid chromatograph as C, the Faraday efficiency FE was calculated from the following formula. FE = n×C×F / (I×t×M) Here, I (A): The constant current passed through the electrode during electrolysis t (s): The electrolysis time C (g / L): The concentration of ethanol measured with the high performance liquid chromatograph F (As / mol): The Faraday constant n: The number of reaction electrons (in the CO2 → ethanol production reaction, 12) M (g / mol): The molecular weight is.

[0046]

Table 1

[0047] In the comparative example, the ethanol production efficiency was as low as 0.3%, and it was not possible to efficiently produce ethanol by reducing CO2. On the other hand, in Invention Examples 1 to 8 of the present invention in which the member main body made of Cu or a Cu alloy and having a porous structure is formed with a nano-Cu structure layer, the ethanol production efficiency was as high as 1.3% or more, and it was possible to efficiently produce ethanol by reducing CO2.

[0048] From the results of the above confirmation experiments, according to the present invention example, it is possible to provide a Cu porous member having sufficient strength, low pressure loss against gases and liquids, and promoting the CO2 reduction reaction to efficiently produce C2 or higher organic compounds such as ethanol. It was confirmed that it is possible.

Explanation of Signs

[0049] 10 Cu porous member 16 nano-Cu structure layer

Claims

1. A Cu porous member comprising a member body made of Cu or a Cu alloy and having a porous structure, and a nano-Cu structure layer formed on at least a part of the surface of the member body. The member body has a porosity in the range of 38% or more and 95% or less, and a thickness in the range of 0.1 mm or more and 1.0 mm or less. The nano-Cu structure layer is formed as a layer by laminating Cu particles having an average length of 20 μm to 1 nm on the surface.

2. The nano-Cu structure layer is formed on one surface side of the member body, and the coverage rate of the nano-Cu structure layer on the one surface of the member body is 20% or more.

3. The Cu particles having an average length of 20 μm to 1 nm constituting the nano-Cu structure layer are in a dendrite shape or a spherical shape.

4. The Cu porous member according to claim 1 or claim 2, wherein the Faraday efficiency when ethanol is generated by using it as an electrode in a co-electrolysis method is 1.0% or more.

Images