JP7521516B2 - Reaction catalyst and electrochemical reactor using the same - Google Patents
Reaction catalyst and electrochemical reactor using the same Download PDFInfo
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- 239000007809 chemical reaction catalyst Substances 0.000 title claims description 25
- 239000011148 porous material Substances 0.000 claims description 69
- 239000003054 catalyst Substances 0.000 claims description 62
- 239000005871 repellent Substances 0.000 claims description 33
- 238000006243 chemical reaction Methods 0.000 claims description 21
- 239000010936 titanium Substances 0.000 claims description 14
- 239000000463 material Substances 0.000 claims description 12
- 239000007788 liquid Substances 0.000 claims description 11
- 239000000126 substance Substances 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 8
- 239000007795 chemical reaction product Substances 0.000 claims description 7
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 6
- 229910052719 titanium Inorganic materials 0.000 claims description 6
- 239000002994 raw material Substances 0.000 claims description 3
- 229910052741 iridium Inorganic materials 0.000 claims description 2
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 claims description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 37
- 239000004810 polytetrafluoroethylene Substances 0.000 description 37
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 30
- 239000001301 oxygen Substances 0.000 description 30
- 229910052760 oxygen Inorganic materials 0.000 description 30
- HTXDPTMKBJXEOW-UHFFFAOYSA-N dioxoiridium Chemical compound O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 25
- 229910000457 iridium oxide Inorganic materials 0.000 description 25
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 22
- 239000003792 electrolyte Substances 0.000 description 22
- 230000000052 comparative effect Effects 0.000 description 20
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 17
- 229910002091 carbon monoxide Inorganic materials 0.000 description 17
- 238000004769 chrono-potentiometry Methods 0.000 description 12
- 229910002092 carbon dioxide Inorganic materials 0.000 description 11
- 239000001569 carbon dioxide Substances 0.000 description 11
- 230000001186 cumulative effect Effects 0.000 description 11
- -1 etc. Substances 0.000 description 10
- 238000006722 reduction reaction Methods 0.000 description 10
- 238000010586 diagram Methods 0.000 description 8
- 239000007789 gas Substances 0.000 description 8
- 239000012528 membrane Substances 0.000 description 8
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 description 8
- 238000002484 cyclic voltammetry Methods 0.000 description 7
- 230000002829 reductive effect Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
- 230000003197 catalytic effect Effects 0.000 description 5
- 238000001035 drying Methods 0.000 description 5
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 4
- 239000000084 colloidal system Substances 0.000 description 4
- 239000008151 electrolyte solution Substances 0.000 description 4
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- 235000019253 formic acid Nutrition 0.000 description 4
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- 230000003287 optical effect Effects 0.000 description 4
- 230000002441 reversible effect Effects 0.000 description 4
- 239000000758 substrate Substances 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229910021607 Silver chloride Inorganic materials 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 3
- 230000002411 adverse Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 230000002452 interceptive effect Effects 0.000 description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 2
- 229910052753 mercury Inorganic materials 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000008055 phosphate buffer solution Substances 0.000 description 2
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 description 1
- 229920000557 Nafion® Polymers 0.000 description 1
- 239000004809 Teflon Substances 0.000 description 1
- 229920006362 Teflon® Polymers 0.000 description 1
- 238000004577 artificial photosynthesis Methods 0.000 description 1
- 239000007853 buffer solution Substances 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000003487 electrochemical reaction Methods 0.000 description 1
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- 229920000515 polycarbonate Polymers 0.000 description 1
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- 229920005989 resin Polymers 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 229920002050 silicone resin Polymers 0.000 description 1
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- Oxygen, Ozone, And Oxides In General (AREA)
- Catalysts (AREA)
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Description
本発明は、反応触媒及びそれを用いた電気化学リアクタに関する。 The present invention relates to a reaction catalyst and an electrochemical reactor using the same.
アノード電極及びカソード電極を備え、その間に電解液を供給し排出する二酸化炭素（ＣＯ２）の電気化学還元リアクタ（太陽電池と組み合わせた人工光合成セルを含む）が知られている（非特許文献１）。このような電気化学還元リアクタにおいて、カソード電極では二酸化炭素（ＣＯ２）が還元されてギ酸、一酸化炭素（ＣＯ）等が生成され、アノード電極では水が酸化されて酸素（Ｏ２）が生成する。例えば、ギ酸を生成する電気化学還元リアクタの例として、アノード電極にはカーボン系のガス拡散電極の電解液側にＰｔ触媒とナフィオンの混合物が塗布された構成が開示されている。 An electrochemical reduction reactor (including an artificial photosynthesis cell combined with a solar cell) for carbon dioxide (CO 2 ) is known that includes an anode electrode and a cathode electrode, between which an electrolyte is supplied and discharged (Non-Patent Document 1). In such an electrochemical reduction reactor, carbon dioxide (CO 2 ) is reduced at the cathode electrode to generate formic acid, carbon monoxide (CO), etc., and water is oxidized at the anode electrode to generate oxygen (O 2 ). For example, as an example of an electrochemical reduction reactor that generates formic acid, a configuration in which a mixture of Pt catalyst and Nafion is applied to the electrolyte side of a carbon-based gas diffusion electrode at the anode electrode has been disclosed.
ところで、電気化学リアクタにおいて、酸素（Ｏ２）が電解液に溶解してカソード電極に到達すると、その一部がカソード電極にて還元されるため、目的である二酸化炭素（ＣＯ２）の還元反応が妨げられる。 In an electrochemical reactor, when oxygen (O 2 ) dissolves in the electrolyte and reaches the cathode electrode, a portion of the oxygen is reduced at the cathode electrode, thereby preventing the target reduction reaction of carbon dioxide (CO 2 ).
また、これら反応の研究は電極面積が１ｃｍ２程度の小型リアクタを用いて行われることが多いが、実用化のためには大型化が必須である。小型リアクタを用いた場合、酸素（Ｏ２）の生成量が少ないのでその悪影響は目立たない。しかしながら、リアクタが大型化すると、電解液に溶解した酸素（Ｏ２）が電解液の下流に蓄積されるので、酸素（Ｏ２）の還元の悪影響が強くなる。 In addition, research into these reactions is often carried out using small reactors with an electrode area of about 1 cm2 , but larger reactors are essential for practical application. When using small reactors, the amount of oxygen ( O2 ) produced is small, so its adverse effects are not noticeable. However, when the reactor is enlarged, oxygen ( O2 ) dissolved in the electrolyte accumulates downstream of the electrolyte, and the adverse effects of the reduction of oxygen ( O2 ) become stronger.
したがって、電気化学リアクタを実用化するためには、反応活性を維持し、外部への電解液の漏れを防ぎつつ、酸素（Ｏ２）の電解液への溶解を抑制して、電気化学リアクタの外部へ適切に排出できる構成が必要である。 Therefore, in order to put an electrochemical reactor into practical use, a configuration is required that can maintain reaction activity, prevent leakage of the electrolyte to the outside, suppress dissolution of oxygen (O 2 ) into the electrolyte, and properly exhaust the oxygen to the outside of the electrochemical reactor.
本発明の１つの態様は、第１面がリアクタ内部の液体、前記第１面とは異なる第２面がリアクタ外部の気体に接した状態において、前記液体に含まれる物質を原料として用いて反応生成物質を生成するために用いられる反応触媒であって、前記液体側に第１親水性多孔質層が配置され、前記気体側に撥水性多孔質層が配置され、前記第１親水性多孔質層と前記撥水性多孔質層との間に前記反応生成物質を生成する反応に利用される触媒を含む触媒多孔質層が配置されていることを特徴とする反応触媒である。 One aspect of the present invention is a reaction catalyst used to generate a reaction product using a substance contained in the liquid as a raw material, with a first surface in contact with a liquid inside a reactor and a second surface different from the first surface in contact with a gas outside the reactor, characterized in that a first hydrophilic porous layer is disposed on the liquid side, a water-repellent porous layer is disposed on the gas side, and a catalyst porous layer containing a catalyst used in a reaction to generate the reaction product is disposed between the first hydrophilic porous layer and the water-repellent porous layer.
ここで、前記触媒多孔質層と前記撥水性多孔質層との間に第２親水性多孔質層が配置されていることが好適である。 Here, it is preferable that a second hydrophilic porous layer is disposed between the catalyst porous layer and the water-repellent porous layer.
また、前記触媒多孔質層は、電気伝導性及び触媒活性を有する多孔質の材料、電気伝導性を有する多孔質の材料に前記触媒を担持した材料、多孔質の材料に電気伝導性と触媒活性を有する物質をコーティングした材料、多孔質の材料に電気伝導性を有する物質をコーティングしたうえに前記触媒を担持した材料、の少なくとも１つを含むことが好適である。 The catalyst porous layer preferably includes at least one of the following: a porous material having electrical conductivity and catalytic activity, a material in which the catalyst is supported on a porous material having electrical conductivity, a material in which a porous material is coated with a substance having electrical conductivity and catalytic activity, and a material in which a porous material is coated with a substance having electrical conductivity and then supports the catalyst.
また、前記第１親水性多孔質層は、空孔の大きさが１μｍ以上８０μｍ以下であることが好適である。特に、前記第１親水性多孔質層は、空孔の大きさが１μｍ以上３０μｍ以下であることが好適である。 The first hydrophilic porous layer preferably has a pore size of 1 μm or more and 80 μm or less. In particular, the first hydrophilic porous layer preferably has a pore size of 1 μm or more and 30 μm or less.
また、前記第１親水性多孔質層は、厚さが８０μｍ以上０．３ｍｍ以下であることが好適である。特に、前記第１親水性多孔質層は、厚さが８０μｍ以上０．２ｍｍ以下であることが好適である。 The first hydrophilic porous layer is preferably 80 μm or more and 0.3 mm or less in thickness. In particular, the first hydrophilic porous layer is preferably 80 μm or more and 0.2 mm or less in thickness.
また、前記触媒多孔質層は、空孔の大きさが１０μｍ以上であることが好適である。特に、前記触媒多孔質層は、空孔の大きさが４０μｍ以上であることが好適である。 It is also preferable that the catalyst porous layer has a pore size of 10 μm or more. In particular, it is preferable that the catalyst porous layer has a pore size of 40 μm or more.
また、前記触媒多孔質層は、面積に対する空孔体積の比、すなわち（空孔体積）／（面積）が０．０１ｃｍ以上であることが好適である。特に、前記触媒多孔質層は、面積に対する空孔体積の比が０．０４ｃｍ以上であることが好適である。 The catalyst porous layer preferably has a pore volume to area ratio, i.e., (pore volume)/(area), of 0.01 cm or more. In particular, the catalyst porous layer preferably has a pore volume to area ratio of 0.04 cm or more.
また、前記撥水性多孔質層は、空孔の平均の大きさが４００μｍ以下であることが好適である。 It is also preferable that the water-repellent porous layer has an average pore size of 400 μm or less.
また、前記撥水性多孔質層は、フッ素樹脂にてコーティングされていることが好適である。 It is also preferable that the water-repellent porous layer is coated with a fluororesin.
また、前記触媒多孔質層は、チタンの多孔体にイリジウムを含む触媒を担持させたものであることが好適である。 It is also preferable that the catalyst porous layer is a porous titanium body carrying a catalyst containing iridium.
また、前記液体は水を含み、水から前記反応生成物質として酸素を生成することが好適である。 It is also preferable that the liquid contains water, and oxygen is produced from the water as the reaction product.
本発明の別の態様は、上記反応触媒を備える電気化学リアクタである。 Another aspect of the present invention is an electrochemical reactor equipped with the above-mentioned reaction catalyst.
本発明によれば、反応活性を維持し、電解液の漏れを防ぎつつ、反応により生成した気体を外部へ適切に排出できる電気化学リアクタを提供することができる。 The present invention provides an electrochemical reactor that can maintain reaction activity, prevent electrolyte leakage, and properly discharge gas generated by the reaction to the outside.
図１及び図２は、本発明の実施の形態における電気化学リアクタ１００を模擬した試験装置の構成を示す模式断面図及び側面図である。なお、図２は、図１のＡ方向からみた側面図を示す。 Figures 1 and 2 are a schematic cross-sectional view and a side view showing the configuration of a test device simulating an electrochemical reactor 100 according to an embodiment of the present invention. Note that Figure 2 shows a side view seen from the direction A in Figure 1.
電気化学リアクタ１００は、セル１０、アノード電極１２、対極１４、参照電極１６及び電解液１８を含んで構成される。 The electrochemical reactor 100 comprises a cell 10, an anode electrode 12, a counter electrode 14, a reference electrode 16, and an electrolyte 18.
アノード電極１２は、図３の分解断面図に示すように、第１親水性多孔質層２０、触媒多孔質層２２及び撥水性多孔質層２６を含んで構成される。具体的には、アノード電極１２は、第１親水性多孔質層２０、触媒多孔質層２２及び撥水性多孔質層２６を積層し、２枚の支持板２８にて挟み込んだ構成とすることができる。すなわち、アノード電極１２は、第１面が電気化学リアクタ１００内部の液体（例えば電解液１８）、第１面とは異なる第２面が電気化学リアクタ１００の外部の気体に接した状態において、液体に含まれる物質を原料として用いて反応生成物質を生成するために用いられる。液体側である第１面に第１親水性多孔質層２０が配置され、気体側である第２面に撥水性多孔質層２６が配置され、第１親水性多孔質層２０と撥水性多孔質層２６との間に反応生成物質を生成する反応に利用される触媒を含む触媒多孔質層２２が配置される。 As shown in the exploded cross-sectional view of FIG. 3, the anode electrode 12 includes a first hydrophilic porous layer 20, a catalyst porous layer 22, and a water-repellent porous layer 26. Specifically, the anode electrode 12 can be configured by stacking the first hydrophilic porous layer 20, the catalyst porous layer 22, and the water-repellent porous layer 26 and sandwiching them between two support plates 28. That is, the anode electrode 12 is used to generate a reaction product using a substance contained in the liquid as a raw material in a state in which the first surface is in contact with a liquid (e.g., electrolyte 18) inside the electrochemical reactor 100 and the second surface different from the first surface is in contact with a gas outside the electrochemical reactor 100. The first hydrophilic porous layer 20 is disposed on the first surface, which is the liquid side, the water-repellent porous layer 26 is disposed on the second surface, which is the gas side, and the catalyst porous layer 22 containing a catalyst used in the reaction to generate the reaction product is disposed between the first hydrophilic porous layer 20 and the water-repellent porous layer 26.
なお、アノード電極１２は、図３に示すように、触媒多孔質層２２と撥水性多孔質層２６との間に第２親水性多孔質層２４を配置してもよい。この場合、アノード電極１２は、第１親水性多孔質層２０、触媒多孔質層２２、第２親水性多孔質層２４及び撥水性多孔質層２６を積層し、２枚の支持板２８にて挟み込んだ構成とする。 As shown in FIG. 3, the anode electrode 12 may have a second hydrophilic porous layer 24 disposed between the catalyst porous layer 22 and the water-repellent porous layer 26. In this case, the anode electrode 12 is configured by stacking the first hydrophilic porous layer 20, the catalyst porous layer 22, the second hydrophilic porous layer 24, and the water-repellent porous layer 26, and sandwiching them between two support plates 28.
アノード電極１２に用いられる触媒は、電気化学リアクタ１００で生じさせる化学反応に寄与する触媒とする。例えば、二酸化炭素（ＣＯ２）を還元してギ酸、一酸化炭素（ＣＯ）を生成する化学反応の場合、アノード電極１２に用いられる触媒は酸化イリジウム（ＩｒＯｘ）ナノコロイド触媒とすることができる。ただし、触媒は、これに限定されるものではなく、電気化学リアクタ１００で必要とされる化学反応を促進させる触媒であればよい。 The catalyst used in the anode electrode 12 is a catalyst that contributes to the chemical reaction occurring in the electrochemical reactor 100. For example, in the case of a chemical reaction in which carbon dioxide (CO 2 ) is reduced to produce formic acid and carbon monoxide (CO), the catalyst used in the anode electrode 12 may be an iridium oxide (IrOx) nanocolloid catalyst. However, the catalyst is not limited to this, and any catalyst that promotes the chemical reaction required in the electrochemical reactor 100 may be used.
本実施の形態では、図４に示すように、第１親水性多孔質層２０、触媒多孔質層２２、第２親水性多孔質層２４及び撥水性多孔質層２６を組み合わせてアノード電極１２を構成した。また、比較例０として、表面を研磨したＴｉ基板にＩｒＯｘナノコロイドを担持したアノード電極１２も用いた。 In this embodiment, as shown in FIG. 4, the anode electrode 12 is formed by combining a first hydrophilic porous layer 20, a catalyst porous layer 22, a second hydrophilic porous layer 24, and a water-repellent porous layer 26. In addition, as Comparative Example 0, an anode electrode 12 in which IrOx nanocolloids are supported on a Ti substrate with a polished surface was also used.
第１親水性多孔質層２０は、空孔の大きさが１μｍ以上８０μｍ以下、より好適には空孔の大きさが１μｍ以上３０μｍ以下である親水性の材料とする。また、第１親水性多孔質層２０は、厚さが８０μｍ以上０．３ｍｍ以下、さらに厚さが８０μｍ以上０．２ｍｍ以下であることが好適である。第１親水性多孔質層２０は、例えば、以下のＴｉｍｅｓｈＡ、ＴｉｍｅｓｈＢ、ＰＴＦＥｍｅｍｂｒａｎｅ１μｍ、ＰＴＦＥｍｅｍｂｒａｎｅ１０μｍから選択することができる。 The first hydrophilic porous layer 20 is a hydrophilic material with a pore size of 1 μm or more and 80 μm or less, more preferably 1 μm or more and 30 μm or less. The first hydrophilic porous layer 20 is preferably a thickness of 80 μm or more and 0.3 mm or less, more preferably 80 μm or more and 0.2 mm or less. The first hydrophilic porous layer 20 can be selected from, for example, the following Timesh A, Timesh B, PTFE membrane 1 μm, and PTFE membrane 10 μm.
ＴｉｍｅｓｈＡは、チタン繊維焼結体（ベカルト東綱メタルファイバー：２ＧＤＬ０６Ｎ－０３０）である。ＴｉｍｅｓｈＡは、厚さ０．３ｍｍ、空孔率７８％、平均孔径６０μｍ、積算細孔容積２０％となる孔径８０μｍ、積算細孔容積８０％となる孔径４０μｍである。図５は、ＴｉｍｅｓｈＡの表面走査電子顕微鏡写真を示す。 Timesh A is a titanium fiber sintered body (Bekaert Toko Metal Fiber: 2GDL06N-030). Timesh A has a thickness of 0.3 mm, a porosity of 78%, an average pore size of 60 μm, a pore size of 80 μm that accounts for 20% of the cumulative pore volume, and a pore size of 40 μm that accounts for 80% of the cumulative pore volume. Figure 5 shows a scanning electron microscope photograph of the surface of Timesh A.
ＴｉｍｅｓｈＢは、チタン繊維焼結体（ベカルト東綱メタルファイバー、２ＧＤＬ１０Ｎ－０２０）である。ＴｉｍｅｓｈＢは、厚さ０．２ｍｍ、空孔率４５％、平均孔径２０μｍ、積算細孔容積２０％となる孔径３０μｍ、積算細孔容積８０％となる孔径１０μｍである。図６は、ＴｉｍｅｓｈＢの表面走査電子顕微鏡写真を示す。 Timesh B is a titanium fiber sintered body (Bekaert Toko Metal Fiber, 2GDL10N-020). Timesh B has a thickness of 0.2 mm, a porosity of 45%, an average pore size of 20 μm, a pore size of 30 μm that accounts for 20% of the cumulative pore volume, and a pore size of 10 μm that accounts for 80% of the cumulative pore volume. Figure 6 shows a scanning electron microscope photograph of the surface of Timesh B.
ＰＴＦＥｍｅｍｂｒａｎｅ１μｍは、親水化処理ＰＴＦＥメンブレン（メルク、オムニポア）である。ＰＴＦＥｍｅｍｂｒａｎｅ１μｍは、厚さ約８０μｍ、平均孔径１μｍである。 PTFE membrane 1 μm is a hydrophilic treated PTFE membrane (Merck, Omnipore). PTFE membrane 1 μm is approximately 80 μm thick and has an average pore size of 1 μm.
ＰＴＦＥｍｅｍｂｒａｎｅ１０μｍは、親水化処理ＰＴＦＥメンブレン（メルク、オムニポア）である。ＰＴＦＥｍｅｍｂｒａｎｅ１０μｍは、厚さ約８０μｍ、平均孔径１０μｍである。 PTFE membrane 10μm is a hydrophilic treated PTFE membrane (Merck, Omnipore). PTFE membrane 10μm is approximately 80μm thick and has an average pore size of 10μm.
触媒多孔質層２２は、電気伝導性及び触媒活性を有する多孔質の材料、電気伝導性を有する多孔質の材料に触媒を担持した材料、多孔質の材料に電気伝導性と触媒活性を有する物質をコーティングした材料、多孔質の材料に電気伝導性を有する物質をコーティングしたうえに触媒を担持した材料から選択することが好適である。触媒多孔質層２２は、厚さが８０μｍ以上０．２ｍｍ以下であることが好適であり、さらに空孔の大きさが４０μｍ以上であることがより好適である。触媒多孔質層２２は、面積に対する空孔体積の比、すなわち（空孔体積）／（面積）が０．０１ｃｍ以上であることが好適であり、さらに面積に対する空孔体積の比が０．０４ｃｍ以上であることがより好適である。例えば、触媒多孔質層２２として、下記のＣＰ＋ＩｒＯｘ、ＴｉｍｅｓｈＡ＋ＩｒＯｘ、ＴｉｍｅｓｈＢ＋ＩｒＯｘ及びｐｏｒｏｕｓＴｉ＋ＩｒＯｘから選択することができる。なお、触媒多孔質層２２は、これらを複数重ね合わせた構成としてもよい。 The catalyst porous layer 22 is preferably selected from a porous material having electrical conductivity and catalytic activity, a material in which a catalyst is supported on a porous material having electrical conductivity, a material in which a porous material is coated with a substance having electrical conductivity and catalytic activity, and a material in which a porous material is coated with a substance having electrical conductivity and then supported with a catalyst. The catalyst porous layer 22 is preferably 80 μm or more and 0.2 mm or less in thickness, and more preferably has a pore size of 40 μm or more. The catalyst porous layer 22 is preferably such that the ratio of the pore volume to the area, i.e., (pore volume)/(area), is 0.01 cm or more, and more preferably the ratio of the pore volume to the area is 0.04 cm or more. For example, the catalyst porous layer 22 can be selected from the following CP+IrOx, TimeshA+IrOx, TimeshB+IrOx, and porousTi+IrOx. The catalyst porous layer 22 may also be constructed by stacking multiple of these.
ＣＰ＋ＩｒＯｘは、カーボンペーパー（東レ、トレカＴＧＰ－Ｈ－０６０）にＩｒＯｘコロイドを滴下・乾燥により担持したものである。ＣＰは、厚さ０．１９ｍｍ、空孔率８０％、平均孔径３０μｍ、積算細孔容積２０％となる孔径４０μｍ、積算細孔容積８０％となる孔径２０μｍである。図７は、ＣＰの表面走査電子顕微鏡写真を示す。 CP+IrOx is a carbon paper (Toray, Torayca TGP-H-060) on which IrOx colloid is supported by dripping and drying. The CP has a thickness of 0.19 mm, a porosity of 80%, an average pore size of 30 μm, a pore size of 40 μm that accounts for 20% of the cumulative pore volume, and a pore size of 20 μm that accounts for 80% of the cumulative pore volume. Figure 7 shows a scanning electron microscope photograph of the surface of the CP.
ＴｉｍｅｓｈＡ＋ＩｒＯｘは、上記ＴｉｍｅｓｈＡにＩｒＯｘコロイドを滴下・乾燥により担持したものである。ＴｉｍｅｓｈＢ＋ＩｒＯｘは、上記ＴｉｍｅｓｈＢにＩｒＯｘコロイドを滴下・乾燥により担持したものである。 Timesh A + IrOx is obtained by dropping IrOx colloid onto the above Timesh A and drying it. Timesh B + IrOx is obtained by dropping IrOx colloid onto the above Timesh B and drying it.
ｐｏｒｏｕｓＴｉ＋ＩｒＯｘは、Ｔｉ多孔質体（長峰製作所、ＭＦ－３０）にＩｒＯｘコロイドを滴下・乾燥により担持したものである。ｐｏｒｏｕｓＴｉは、厚さ１ｍｍ、空孔率８８％、平均孔径３８０ｍｍである。図８は、ｐｏｒｏｕｓＴｉの光学顕微鏡写真を示す。 PorousTi+IrOx is a porous Ti material (Mf-30, Nagamine Seisakusho) on which IrOx colloids are supported by dripping and drying. The porous Ti has a thickness of 1 mm, a porosity of 88%, and an average pore size of 380 mm. Figure 8 shows an optical microscope photograph of the porous Ti.
第２親水性多孔質層２４は、空孔の大きさが１μｍ以上８０μｍ以下、より好適には空孔の大きさが１μｍ以上３０μｍ以下である親水性の材料とする。また、第１親水性多孔質層２０は、厚さが８０μｍ以上０．３ｍｍ以下、さらに厚さが８０μｍ以上０．２ｍｍ以下であることが好適である。第２親水性多孔質層２４は、例えば、ＴｉｍｅｓｈＡ、ｐｏｒｏｕｓＴｉ、ＴｉｍｅｓｈＡ＋ｓｕｒｆａｃｅＰＴＦＥ及びＴｉｍｅｓｈＡ＋ＩｒＯｘ＋ｓｕｒｆａｃｅＰＴＦＥから選択することができる。なお、第２親水性多孔質層２４は適宜設けない構成としてもよい。 The second hydrophilic porous layer 24 is a hydrophilic material with a pore size of 1 μm or more and 80 μm or less, more preferably 1 μm or more and 30 μm or less. The first hydrophilic porous layer 20 is preferably 80 μm or more and 0.3 mm or less in thickness, more preferably 80 μm or more and 0.2 mm or less in thickness. The second hydrophilic porous layer 24 can be selected from, for example, TimeshA, porousTi, TimeshA + surface PTFE, and TimeshA + IrOx + surface PTFE. The second hydrophilic porous layer 24 may be omitted as appropriate.
ＴｉｍｅｓｈＡ＋ｓｕｒｆａｃｅＰＴＦＥは、上記ＴｉｍｅｓｈＡの表面にポリテトラフルオロエチレン（ＰＴＦＥ：ｐｏｌｙｔｅｔｒａｆｌｕｏｒｏｅｔｈｙｌｅｎｅ）をコーティングしたものである。ＴｉｍｅｓｈＡ＋ｓｕｒｆａｃｅＰＴＦＥを用いる場合、ＰＴＦＥがコーティングされた面を大気側に配置することが必要である。ＰＴＦＥコーティングが撥水性多孔質層２６の機能を備える。 TimeshA+surfacePTFE is the above TimeshA surface coated with polytetrafluoroethylene (PTFE). When using TimeshA+surfacePTFE, it is necessary to place the PTFE-coated surface on the atmospheric side. The PTFE coating provides the function of the water-repellent porous layer 26.
ＴｉｍｅｓｈＡ＋ＩｒＯｘ＋ｓｕｒｆａｃｅＰＴＦＥは、上記ＴｉｍｅｓｈＡ＋ＩｒＯｘの表面にポリテトラフルオロエチレン（ＰＴＦＥ）をコーティングしたものである。ＴｉｍｅｓｈＡ＋ＩｒＯｘ＋ｓｕｒｆａｃｅＰＴＦＥを用いる場合、ＰＴＦＥがコーティングされた面を大気側に配置することが必要である。ＰＴＦＥコーティングが撥水性多孔質層２６の機能を備える。 TimeshA+IrOx+surfacePTFE is the above TimeshA+IrOx coated with polytetrafluoroethylene (PTFE). When using TimeshA+IrOx+surfacePTFE, it is necessary to place the PTFE-coated surface on the atmospheric side. The PTFE coating provides the function of the water-repellent porous layer 26.
撥水性多孔質層２６は、撥水性を有する多孔体で構成される。撥水性多孔質層２６は、例えば、フッ素樹脂にてコーティングされている多孔体とすることができる。撥水性多孔質層２６は、空孔の平均の大きさが４００μｍ以下であることが好適である。撥水性多孔質層２６は、例えば、ＣＰ＋ＰＴＦＥ、ＰＴＦＥｎｅｔ及びＴｉｍｅｓｈＡ＋ＰＴＦＥから選択することができる。なお、第２親水性多孔質層２４としてポリテトラフルオロエチレン（ＰＴＦＥ）をコーティングしたＴｉｍｅｓｈＡ＋ｓｕｒｆａｃｅＰＴＦＥ又はＴｉｍｅｓｈＡ＋ＩｒＯｘ＋ｓｕｒｆａｃｅＰＴＦＥを用いた場合には撥水性多孔質層２６を設けない構成としてもよい。 The water-repellent porous layer 26 is composed of a porous body having water repellency. The water-repellent porous layer 26 can be, for example, a porous body coated with a fluororesin. The water-repellent porous layer 26 preferably has an average pore size of 400 μm or less. The water-repellent porous layer 26 can be selected from, for example, CP+PTFE, PTFEnet, and TimeshA+PTFE. Note that when TimeshA+surfacePTFE or TimeshA+IrOx+surfacePTFE coated with polytetrafluoroethylene (PTFE) is used as the second hydrophilic porous layer 24, the water-repellent porous layer 26 may not be provided.
ＣＰ＋ＰＴＦＥは、カーボンペーパーにポリテトラフルオロエチレン（ＰＴＦＥ）をコーティングしたものである（ケミックス、ＴＧＰ－Ｈ－０６０Ｈ）。ＣＰ＋ＰＴＦＥは、厚さ０．１９ｍｍ、空孔率８０％、平均孔径３０μｍ、積算細孔容積２０％となる孔径４０μｍ、積算細孔容積８０％となる孔径２０μｍであった。図９は、ＣＰ＋ＰＴＦＥの表面走査電子顕微鏡写真を示す。 CP+PTFE is carbon paper coated with polytetrafluoroethylene (PTFE) (Chemix, TGP-H-060H). CP+PTFE had a thickness of 0.19 mm, a porosity of 80%, an average pore size of 30 μm, a pore size of 40 μm that accounts for 20% of the cumulative pore volume, and a pore size of 20 μm that accounts for 80% of the cumulative pore volume. Figure 9 shows a scanning electron microscope photograph of the surface of CP+PTFE.
ＰＴＦＥｎｅｔは、４３メッシュ相当のポリテトラフルオロエチレン（ＰＴＦＥ）のネット（フロン工業、Ｆ－３２６１－００６）である。ＰＴＦＥｎｅｔは、厚さ０．４ｍｍ、空孔率３２％、平均孔径４００μｍであった。図１０は、ＰＴＦＥｎｅｔの表面光学顕微鏡写真を示す。 PTFEnet is a polytetrafluoroethylene (PTFE) net equivalent to 43 mesh (Flon Industries, F-3261-006). PTFEnet had a thickness of 0.4 mm, a porosity of 32%, and an average pore size of 400 μm. Figure 10 shows an optical microscope photograph of the surface of PTFEnet.
ＴｉｍｅｓｈＡ＋ＰＴＦＥは、上記ＴｉｍｅｓｈＡにポリテトラフルオロエチレン（ＰＴＦＥ）分散液（ケミックス、テフロン（登録商標）ディスパージョン）への浸漬、乾燥、焼成によりポリテトラフルオロエチレン（ＰＴＦＥ）をコーティングしたものである。ＴｉｍｅｓｈＡ＋ＰＴＦＥは、厚さ０．３ｍｍ、空孔率７８％、平均孔径６０μｍであった。なお、ＰＴＦＥｎｅｔの平均孔径は、メッシュの菱形の貫通孔の断面積を円筒に換算したときの直径とした。 Timesh A + PTFE is obtained by coating the above Timesh A with polytetrafluoroethylene (PTFE) by immersing it in a polytetrafluoroethylene (PTFE) dispersion (Chemix, Teflon (registered trademark) dispersion), drying, and baking. Timesh A + PTFE had a thickness of 0.3 mm, a porosity of 78%, and an average pore size of 60 μm. The average pore size of the PTFE net was the diameter of the cross-sectional area of the diamond-shaped through holes in the mesh converted into a cylinder.
ここで、上記の構成要素において、積算細孔容積と孔径との関係は、水銀ポロシメータ（アントンパール、ＰｏｒｅＭａｓｔｅｒ ６０ＧＴ）により測定した。積算細孔容積が大きい方から積算細孔容積の相対値が２０％、５０％（平均孔径）、８０％となるときの孔径を求めた。測定時の水銀パラメータは、表面張力：４８０ｍＮ／ｍ、接触角：１３５ｄｅｇｒｅｅｓを使用した。ただし、ｐｏｒｏｕｓＴｉの孔径はメーカーのカタログ値である。 Here, the relationship between the cumulative pore volume and pore size in the above components was measured using a mercury porosimeter (Anton Paar, PoreMaster 60GT). The pore sizes were determined when the relative cumulative pore volume was 20%, 50% (average pore size), and 80% from the largest cumulative pore volume. The mercury parameters used during measurement were surface tension: 480 mN/m, contact angle: 135 degrees. However, the pore size of porous Ti is the manufacturer's catalog value.
支持板２８は、アノード電極１２を構成する第１親水性多孔質層２０、触媒多孔質層２２、第２親水性多孔質層２４及び撥水性多孔質層２６の積層体を支持する部材である。支持板２８は、アノード電極１２を保持する機械的な強度と化学反応に対する耐性を有する部材であれば特に限定されるものではないが、例えば樹脂、ガラス、金属とすることができる。支持板２８は、例えば、ポリカーボネートとすることができる。支持板２８は、電解液１８及び反応で発生した気体を通過させるための開口穴を有する。 The support plate 28 is a member that supports the laminate of the first hydrophilic porous layer 20, the catalyst porous layer 22, the second hydrophilic porous layer 24, and the water-repellent porous layer 26 that constitute the anode electrode 12. The support plate 28 is not particularly limited as long as it has the mechanical strength to hold the anode electrode 12 and resistance to chemical reactions, but can be, for example, resin, glass, or metal. The support plate 28 can be, for example, polycarbonate. The support plate 28 has openings to allow the electrolyte 18 and gas generated by the reaction to pass through.
電解液１８は、電気化学リアクタ１００で生じる化学反応に適した液体とすればよい。例えば、二酸化炭素（ＣＯ２）を還元してギ酸、一酸化炭素（ＣＯ）を生成する化学反応の場合、電解液１８は、リン酸緩衝水溶液やホウ酸緩衝水溶液とすることが好適である。 The electrolyte 18 may be any liquid suitable for the chemical reaction occurring in the electrochemical reactor 100. For example, in the case of a chemical reaction in which carbon dioxide (CO 2 ) is reduced to produce formic acid and carbon monoxide (CO), the electrolyte 18 is preferably an aqueous phosphate buffer solution or an aqueous borate buffer solution.
［実施例及び比較例］
以下、二酸化炭素（ＣＯ２）を還元する電気化学リアクタ１００の実施例及び比較例に
ついて説明する。
[Examples and Comparative Examples]
Hereinafter, examples and comparative examples of the electrochemical reactor 100 for reducing carbon dioxide (CO 2 ) will be described.
電気化学リアクタ１００のセル１０は、電気化学反応の評価に用いられるＨ型セルの片側に似た形状のガラスセル（イーシーフロンティア、プレート電極評価セル、ＶＭ４）を用いた。 Cell 10 of the electrochemical reactor 100 was a glass cell (EC Frontier, plate electrode evaluation cell, VM4) with a shape similar to one side of an H-shaped cell used to evaluate electrochemical reactions.
アノード電極１２として、第１親水性多孔質層２０、触媒多孔質層２２、第２親水性多孔質層２４及び撥水性多孔質層２６の積層体を２枚の支持板２８で挟み込み、シリコーン樹脂を用いて周囲を封止して形成した作用極を用いた。第１親水性多孔質層２０、触媒多孔質層２２、第２親水性多孔質層２４及び撥水性多孔質層２６は、それぞれ図４に示す組み合わせとした。また、比較例０として、表面を研磨したチタン（Ｔｉ）基板に酸化イリジウム（ＩｒＯｘ）ナノコロイドを担持したアノード電極１２を用いた。支持板２８は、それぞれに直径１１ｍｍの開口部を設けた構成とした。アノード電極１２は、セル１０の側面に設けられた開口部に取り付けた。 As the anode electrode 12, a working electrode was used, which was formed by sandwiching a laminate of a first hydrophilic porous layer 20, a catalyst porous layer 22, a second hydrophilic porous layer 24, and a water-repellent porous layer 26 between two support plates 28 and sealing the periphery with silicone resin. The first hydrophilic porous layer 20, the catalyst porous layer 22, the second hydrophilic porous layer 24, and the water-repellent porous layer 26 were combined as shown in FIG. 4. In addition, as Comparative Example 0, an anode electrode 12 was used in which iridium oxide (IrOx) nanocolloids were supported on a titanium (Ti) substrate with a polished surface. Each of the support plates 28 was configured to have an opening with a diameter of 11 mm. The anode electrode 12 was attached to an opening provided on the side of the cell 10.
また、対極１４としてＰｔ対極、参照電極１６としてＡｇ／ＡｇＣｌ参照極を用いて３極型電気化学セルを構成した。参照極及び対極は、セル１０の上側に設けられた開口部より挿入した。電解液１８としては、０．４Ｍリン酸緩衝水溶液を用いた。 A three-electrode electrochemical cell was constructed using a Pt counter electrode as the counter electrode 14 and an Ag/AgCl reference electrode as the reference electrode 16. The reference electrode and counter electrode were inserted from an opening provided on the upper side of the cell 10. A 0.4 M phosphate buffer solution was used as the electrolyte 18.
このような電気化学リアクタ１００についてポテンショ／ガルバノスタットを用いてサイクリックボルタンメトリー（ＣＶ）測定を行い、ＣＶカーブを取得した。電位の走査範囲は０～２．０Ｖｖｓ．Ａｇ／ＡｇＣｌ、走査速度は１０ｍＶ／ｓに設定した。さらに、電流１５ｍＡの条件でクロノポテンショメトリー（ＣＰ）測定を行い、電解液側に排出される酸素（Ｏ２）量を比較例（酸素（Ｏ２）が全て電解液側に排出される）の場合と比較して酸素（Ｏ２）がセルの外部である大気側へ排出される比率を求めた。なお、この際、何れの試料についても、大気側への電解液の滲み出しは目視では確認されなかった。 Cyclic voltammetry (CV) measurements were performed on such an electrochemical reactor 100 using a potentio/galvanostat to obtain a CV curve. The potential scanning range was set to 0 to 2.0 V vs. Ag/AgCl, and the scanning speed was set to 10 mV/s. Furthermore, chronopotentiometry (CP) measurements were performed under a current condition of 15 mA, and the amount of oxygen (O 2 ) discharged to the electrolyte side was compared with the comparative example (where all oxygen (O 2 ) was discharged to the electrolyte side) to determine the ratio of oxygen (O 2 ) discharged to the atmosphere side, which is outside the cell. At this time, for any of the samples, seepage of the electrolyte to the atmosphere side was not visually confirmed.
比較例０のように、チタン（Ｔｉ）基板に酸化イリジウム（ＩｒＯｘ）ナノコロイドを担持した試料の場合、電位の順方向の走査（増大）に伴い、およそ０．９Ｖｖｓ．Ａｇ／ＡｇＣｌから直線的に電流が増大し、電位が２．０Ｖのときに電流は２６ｍＡに達した。その後、電位を逆方向に走査（減少）すると、順方向とほぼ同じ線上をたどって電流が減少した。即ち、図１１に示すように、ＣＶカーブにヒステリシスは見られなかった。 In the case of a sample in which iridium oxide (IrOx) nanocolloids were supported on a titanium (Ti) substrate, as in Comparative Example 0, the current increased linearly from approximately 0.9 V vs. Ag/AgCl as the potential was scanned (increased) in the forward direction, and reached 26 mA when the potential was 2.0 V. When the potential was then scanned (decreased) in the reverse direction, the current decreased along almost the same line as in the forward direction. In other words, as shown in Figure 11, no hysteresis was observed in the CV curve.
従来技術に近い構成である比較例１の場合、比較例０に近いＣＶカーブが得られたものの、酸素（Ｏ２）の大気側排出率は４０％であった。すなわち、触媒多孔質層２２にて生成した酸素（Ｏ２）は、セルの外部である大気側には一部しか十分に排出されなかった。電解液１８の側に第１親水性多孔質層２０を加えた比較例２の場合、酸素（Ｏ２）の大気側排出率は９５％以上に向上した。しかしながら、比較例２の場合、ＣＶ測定における順方向走査時の電流が大幅に低下し、逆方向走査時の電流は更に低下した。すなわち、ＣＶカーブにヒステリシスが生じた。 In the case of Comparative Example 1, which has a configuration close to the conventional technology, a CV curve close to that of Comparative Example 0 was obtained, but the oxygen (O 2 ) discharge rate to the atmosphere was 40%. That is, only a portion of the oxygen (O 2 ) generated in the catalyst porous layer 22 was sufficiently discharged to the atmosphere outside the cell. In the case of Comparative Example 2, in which the first hydrophilic porous layer 20 was added to the electrolyte 18 side, the oxygen (O 2 ) discharge rate to the atmosphere was improved to 95% or more. However, in the case of Comparative Example 2, the current during forward scanning in the CV measurement was significantly reduced, and the current during reverse scanning was further reduced. That is, hysteresis occurred in the CV curve.
電位を順方向に走査すると、酸素（Ｏ２）の気泡の発生量が徐々に増大する。これが速やかに排出されずにアノード電極１２の触媒多孔質層２２内に滞留すると、触媒（ＩｒＯｘ）の表面が一部覆われて反応に対する実効的な面積が低下し、酸素（Ｏ２）と共に生成される水素イオン（Ｈ＋）のカソードへの伝搬経路が狭くなって伝搬が妨げられて電流が低下する。その結果、大量の酸素（Ｏ２）の気泡が発生した後の逆方向電位走査時には順方向時に比べて電流が低下する。 When the potential is scanned in the forward direction, the amount of oxygen ( O2 ) bubbles generated gradually increases. If these are not quickly discharged and remain in the catalytic porous layer 22 of the anode electrode 12, the surface of the catalyst (IrOx) is partially covered, reducing the effective area for the reaction, narrowing the propagation path of hydrogen ions (H + ) generated together with oxygen ( O2 ) to the cathode, hindering propagation and reducing the current. As a result, the current is lower during reverse potential scanning after a large amount of oxygen ( O2 ) bubbles are generated than during forward potential scanning.
本実施の形態では、電気化学リアクタ１００の電気特性を評価する指数として電流ＩＦ及び規格化電流比（ＩＦ－ＩＢ）／ＩＦを用いた。すなわち、気泡滞留の影響が小さい順方向走査時における電位１．３Ｖ時の電流（ＩＦ）を反応活性の指標とし、気泡滞留の影響が大きくなった逆方向走査時における電位１．３Ｖの電流（ＩＢ）との差を規格化した規格化電流比（ＩＦ－ＩＢ）／ＩＦを酸素（Ｏ２）の気泡の滞留の有無の指標として用いた。電流ＩＦが大きいほど、規格化電流比（ＩＦ－ＩＢ）／ＩＦが小さいほど電気化学リアクタ１００の電気特性が優れていると判断できる。 In this embodiment, the current I F and the normalized current ratio (I F -I B )/I F were used as indices for evaluating the electrical characteristics of the electrochemical reactor 100. That is, the current (I F ) at a potential of 1.3 V during forward scanning, when the influence of bubble retention is small, was used as an index of reaction activity, and the normalized current ratio (I F -I B ) /I F , which is a normalized difference between the current (I F ) at a potential of 1.3 V during reverse scanning, when the influence of bubble retention is large, was used as an index of the presence or absence of oxygen (O 2 ) bubble retention. It can be determined that the electrical characteristics of the electrochemical reactor 100 are better when the current I F is larger and the normalized current ratio (I F -I B )/I F is smaller.
図４に、比較例０～４及び実施例１～１３の評価結果をまとめて示す。第１親水性多孔質層２０及び第２親水性多孔質層２４を備えない比較例３及び比較例４では電流ＩＦ及び規格化電流比（ＩＦ－ＩＢ）／ＩＦが比較例０に近く、比較的良好な値を示したが、酸素（Ｏ２）の大気側排出率が比較例１に近い値であり、実施例１～１３に比べて低かった。 4 shows the evaluation results of Comparative Examples 0 to 4 and Examples 1 to 13. In Comparative Example 3 and Comparative Example 4, which do not have the first hydrophilic porous layer 20 and the second hydrophilic porous layer 24, the current I F and the normalized current ratio (I F -I B )/I F were close to those of Comparative Example 0 and showed relatively good values, but the discharge rate of oxygen (O 2 ) to the atmosphere was close to that of Comparative Example 1 and was lower than those of Examples 1 to 13.
比較例０～４に対して、第１親水性多孔質層２０、触媒多孔質層２２及び撥水性多孔質層２６を備えた実施例１～３，５及び第１親水性多孔質層２０、触媒多孔質層２２、第２親水性多孔質層２４及び撥水性多孔質層２６を備えた実施例６～１４は、酸素（Ｏ２）の大気側排出率が９５％以上を実現しながら、電流ＩＦ及び規格化電流比（ＩＦ－ＩＢ）／ＩＦの両方の観点から比較例２よりも優れた特性を示した。第１親水性多孔質層２０、触媒多孔質層２２、第２親水性多孔質層２４及び撥水性多孔質層２６を備えた実施例４は、電流ＩＦの観点からは比較例２と同等、規格化電流比（ＩＦ－ＩＢ）／ＩＦの観点からは比較例２よりも優れた特性であった。特に、実施例５～１４では、電流ＩＦ及び規格化電流比（ＩＦ－ＩＢ）／ＩＦの両方の観点から比較例０と同等又はそれを上回る優れた特性を示した。 In comparison with Comparative Examples 0 to 4, Examples 1 to 3 and 5 including the first hydrophilic porous layer 20, the catalyst porous layer 22, and the water-repellent porous layer 26, and Examples 6 to 14 including the first hydrophilic porous layer 20, the catalyst porous layer 22, the second hydrophilic porous layer 24, and the water-repellent porous layer 26, achieved an atmospheric discharge rate of oxygen (O 2 ) of 95% or more, and showed superior characteristics to Comparative Example 2 in terms of both current I F and normalized current ratio (I F -I B )/I F. Example 4 including the first hydrophilic porous layer 20, the catalyst porous layer 22, the second hydrophilic porous layer 24, and the water-repellent porous layer 26 showed characteristics equivalent to Comparative Example 2 in terms of current I F , and superior characteristics to Comparative Example 2 in terms of normalized current ratio (I F -I B )/I F. In particular, Examples 5 to 14 showed superior characteristics equivalent to or exceeding those of Comparative Example 0 in terms of both current I F and normalized current ratio (I F -I B )/I F.
以上のように、本実施の形態におけるアノード電極１２では、生成した気体物質の９５％以上が電解液１８の反対側（大気側）、すなわちセルの外部に排出された。二酸化炭素（ＣＯ２）の還元反応のための電気化学リアクタ１００に本実施の形態におけるアノード電極１２を適用した場合、二酸化炭素（ＣＯ２）の還元反応では水の酸化反応により生成された酸素（Ｏ２）が反対側の対極１４に到達して反応し、目的である二酸化炭素（ＣＯ２）の還元反応を妨げることを抑制することができる。その結果、二酸化炭素（ＣＯ２）の還元反応の効率が向上する。 As described above, in the anode electrode 12 of the present embodiment, 95% or more of the generated gaseous material is discharged to the opposite side (atmosphere side) of the electrolytic solution 18, i.e., to the outside of the cell. When the anode electrode 12 of the present embodiment is applied to the electrochemical reactor 100 for the reduction reaction of carbon dioxide (CO 2 ), oxygen (O 2 ) generated by the oxidation reaction of water in the reduction reaction of carbon dioxide (CO 2 ) reaches the counter electrode 14 on the opposite side and reacts therewith, which can be prevented from interfering with the target reduction reaction of carbon dioxide (CO 2 ). As a result, the efficiency of the reduction reaction of carbon dioxide (CO 2 ) is improved.
また、電解液１８に大量の酸素（Ｏ２）が含まれることを防ぎ、電気化学リアクタ１００に電解液１８を供給及び排出する際において背圧の上昇を抑制することができる。その結果、電解液１８の供給及び排出のためのポンプの消費電力が抑制される。 In addition, it is possible to prevent a large amount of oxygen (O 2 ) from being contained in the electrolytic solution 18, and to suppress an increase in back pressure when the electrolytic solution 18 is supplied to and discharged from the electrochemical reactor 100. As a result, the power consumption of the pump for supplying and discharging the electrolytic solution 18 is suppressed.
また、酸素（Ｏ２）がアノード電極１２に用いられる触媒表面に付着して反応基質である水の供給が妨げられることを抑制することができる。その結果、水の酸化反応の効率が向上する。 It is also possible to prevent oxygen (O 2 ) from adhering to the surface of the catalyst used in the anode electrode 12 and interfering with the supply of water, which is a reaction substrate, thereby improving the efficiency of the water oxidation reaction.
さらに、電気化学リアクタ１００内に大量の酸素（Ｏ２）の気泡が発生して内圧が上昇することを防ぐことができる。その結果、電気化学リアクタ１００のセル１０に求められる耐圧が小さくなり、電気化学リアクタ１００を軽量化及び低コスト化することができる。 Furthermore, it is possible to prevent a rise in internal pressure caused by the generation of a large amount of oxygen (O 2 ) bubbles in the electrochemical reactor 100. As a result, the withstand pressure required for the cells 10 of the electrochemical reactor 100 is reduced, and the electrochemical reactor 100 can be made lighter and less expensive.
これらの作用及び効果が生じる理由として、適切な空孔サイズをもつ第１親水性多孔質層２０により、生成された酸素（Ｏ２）の気泡の電解液１８側への伝搬が抑えられたためと推察される。同時に、反応の継続のために必要な酸素（Ｏ２）と共に生成する水素イオン（Ｈ＋）の電解液１８への伝搬も妨げられなかったと推察される。また、必要な空孔サイズと空孔体積をもつ触媒多孔質層２２又は触媒多孔質層２２及び第２親水性多孔質層２４の組み合わせによって、生成された酸素（Ｏ２）の気泡が触媒材料表面を覆って反応を妨げることなく、撥水性多孔質層２６を通過して電気化学リアクタ１００の外部へ排出されたためと推察される。このとき、適切な空孔サイズをもつ撥水性多孔質層２６を用いることによって、電解液１８が外部へ漏れ出すことなく、生成された酸素（Ｏ２）の気泡のみが外部へ排出される。 It is presumed that the reason for these actions and effects is that the first hydrophilic porous layer 20 having an appropriate pore size suppresses the propagation of the generated oxygen (O 2 ) bubbles to the electrolyte 18 side. At the same time, it is presumed that the propagation of the hydrogen ions (H + ) generated together with the oxygen (O 2 ) necessary for the continuation of the reaction to the electrolyte 18 is not hindered. It is also presumed that the catalyst porous layer 22 having the necessary pore size and pore volume or the combination of the catalyst porous layer 22 and the second hydrophilic porous layer 24 allows the generated oxygen (O 2 ) bubbles to pass through the water-repellent porous layer 26 and be discharged to the outside of the electrochemical reactor 100 without covering the surface of the catalyst material and hindering the reaction. At this time, by using the water-repellent porous layer 26 having an appropriate pore size, the electrolyte 18 does not leak to the outside, and only the generated oxygen (O 2 ) bubbles are discharged to the outside.
なお、本実施の形態では、二酸化炭素（ＣＯ２）の還元反応によって酸素（Ｏ２）を発生させる電気化学リアクタ１００を例として説明したが、アノード電極１２の適用範囲はこれに限定されるものではない。すなわち、触媒多孔質層２２に担持された触媒の作用によってなんらかの気体を発生させる反応に用いられる電気化学リアクタ１００であればアノード電極１２の適用範囲となる。このとき、アノード電極１２の触媒多孔質層２２に担持させる触媒は、電気化学リアクタ１００の目的となる反応に寄与する触媒とすればよい。 In this embodiment, the electrochemical reactor 100 that generates oxygen (O 2 ) by a reduction reaction of carbon dioxide (CO 2 ) has been described as an example, but the application range of the anode electrode 12 is not limited to this. In other words, the application range of the anode electrode 12 is any electrochemical reactor 100 that is used in a reaction that generates some kind of gas by the action of a catalyst supported in the catalyst porous layer 22. In this case, the catalyst supported in the catalyst porous layer 22 of the anode electrode 12 may be a catalyst that contributes to the target reaction of the electrochemical reactor 100.
１０ セル、１２ アノード電極、１４ 対極、１６ 参照電極、１８ 電解液、２０ 第１親水性多孔質層、２２ 触媒多孔質層、２４ 第２親水性多孔質層、２６ 撥水性多孔質層、２８ 支持板、１００ 電気化学リアクタ。 10 cell, 12 anode electrode, 14 counter electrode, 16 reference electrode, 18 electrolyte, 20 first hydrophilic porous layer, 22 catalyst porous layer, 24 second hydrophilic porous layer, 26 water-repellent porous layer, 28 support plate, 100 electrochemical reactor.
Claims (13)
前記液体側に第１親水性多孔質層が配置され、前記気体側に撥水性多孔質層が配置され、前記第１親水性多孔質層と前記撥水性多孔質層との間に前記反応生成物質を生成する反応に利用される触媒を含む触媒多孔質層が配置されており、前記触媒多孔質層と前記撥水性多孔質層との間に第２親水性多孔質層が配置されており、
前記触媒多孔質層は、電気伝導性を有するチタンの多孔体に前記触媒を担持した材料からなることを特徴とする反応触媒。 A reaction catalyst used to generate a reaction product substance using a substance contained in a liquid as a raw material in a state in which a first surface is in contact with a liquid containing water and a second surface different from the first surface is in contact with a gas, the reaction catalyst comprising:
a first hydrophilic porous layer is disposed on the liquid side, a water-repellent porous layer is disposed on the gas side, a catalyst porous layer containing a catalyst utilized in a reaction for generating the reaction product is disposed between the first hydrophilic porous layer and the water-repellent porous layer, and a second hydrophilic porous layer is disposed between the catalyst porous layer and the water-repellent porous layer,
The catalyst porous layer is made of a material in which the catalyst is supported on a porous body of electrically conductive titanium.
前記第１親水性多孔質層は、空孔の大きさが１μｍ以上８０μｍ以下であることを特徴とする反応触媒。 The reaction catalyst according to claim 1 ,
A reaction catalyst, wherein the first hydrophilic porous layer has a pore size of 1 μm or more and 80 μm or less.
前記第１親水性多孔質層は、空孔の大きさが１μｍ以上３０μｍ以下であることを特徴とする反応触媒。 The reaction catalyst according to claim 2 ,
A reaction catalyst, wherein the first hydrophilic porous layer has a pore size of 1 μm or more and 30 μm or less.
前記第１親水性多孔質層は、厚さが８０μｍ以上０．３ｍｍ以下であることを特徴とする反応触媒。 The reaction catalyst according to any one of claims 1 to 3 ,
The reaction catalyst, wherein the first hydrophilic porous layer has a thickness of 80 μm or more and 0.3 mm or less.
前記第１親水性多孔質層は、厚さが８０μｍ以上０．２ｍｍ以下であることを特徴とする反応触媒。 The reaction catalyst according to claim 4 ,
The reaction catalyst, wherein the first hydrophilic porous layer has a thickness of 80 μm or more and 0.2 mm or less.
前記触媒多孔質層は、空孔の大きさが１０μｍ以上であることを特徴とする反応触媒。 The reaction catalyst according to any one of claims 1 to 5 ,
The catalyst porous layer has a pore size of 10 μm or more.
前記触媒多孔質層は、空孔の大きさが４０μｍ以上であることを特徴とする反応触媒。 The reaction catalyst according to claim 6 ,
The catalyst porous layer has a pore size of 40 μm or more.
前記触媒多孔質層は、面積に対する空孔体積の比［（空孔体積）／（面積）］が０．０１ｃｍ以上であることを特徴とする反応触媒。 The reaction catalyst according to any one of claims 1 to 7 ,
The catalyst porous layer has a pore volume to area ratio [(pore volume)/(area)] of 0.01 cm or more.
前記触媒多孔質層は、面積に対する空孔体積の比［（空孔体積）／（面積）］が０．０４ｃｍ以上であることを特徴とする反応触媒。 The reaction catalyst according to claim 8 ,
The catalyst porous layer has a pore volume to area ratio [(pore volume)/(area)] of 0.04 cm or more.
前記撥水性多孔質層は、空孔の平均の大きさが４００μｍ以下であることを特徴とする反応触媒。 The reaction catalyst according to any one of claims 1 to 9 ,
A reaction catalyst, wherein the water-repellent porous layer has an average pore size of 400 μm or less.
前記撥水性多孔質層は、フッ素樹脂にてコーティングされていることを特徴とする反応触媒。 The reaction catalyst according to any one of claims 1 to 10 ,
The reaction catalyst is characterized in that the water-repellent porous layer is coated with a fluororesin.
前記触媒多孔質層は、イリジウムを含む触媒を担持させたものであることを特徴とする反応触媒。 The reaction catalyst according to any one of claims 1 to 11 ,
The reaction catalyst is characterized in that the catalyst porous layer supports a catalyst containing iridium.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2011029171A (en) | 2009-06-26 | 2011-02-10 | Nissan Motor Co Ltd | Gas diffusion electrode and production method for same, membrane electrode assembly, and production method for same |
| JP2014165056A (en) | 2013-02-26 | 2014-09-08 | Imura Zairyo Kaihatsu Kenkyusho:Kk | Positive electrode for metal air secondary battery |
| JP2019056136A (en) | 2017-09-20 | 2019-04-11 | 株式会社東芝 | Electrochemical reactor |
| JP2021059760A (en) | 2019-10-08 | 2021-04-15 | 株式会社豊田中央研究所 | Co2 reductive reaction apparatus |
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| JP6344823B2 (en) * | 2015-09-18 | 2018-06-20 | 日本電信電話株式会社 | Lithium-air secondary battery and method for manufacturing air electrode for lithium secondary battery |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2011029171A (en) | 2009-06-26 | 2011-02-10 | Nissan Motor Co Ltd | Gas diffusion electrode and production method for same, membrane electrode assembly, and production method for same |
| JP2014165056A (en) | 2013-02-26 | 2014-09-08 | Imura Zairyo Kaihatsu Kenkyusho:Kk | Positive electrode for metal air secondary battery |
| JP2019056136A (en) | 2017-09-20 | 2019-04-11 | 株式会社東芝 | Electrochemical reactor |
| JP2021059760A (en) | 2019-10-08 | 2021-04-15 | 株式会社豊田中央研究所 | Co2 reductive reaction apparatus |
Non-Patent Citations (1)
| Title |
|---|
| WHUPPLE et al.，Microfluidic Reactor for the Electrochemical Reduction of Carbon Dioxide :The Effect of pH，Electrochemical and Solid -State Letters，2010年，Vol.13, No.9，p.B109-B111 |
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