JP6713121B2 - Carbon dioxide reduction device and reduction method - Google Patents
Carbon dioxide reduction device and reduction method Download PDFInfo
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 title claims description 146
- 229910002092 carbon dioxide Inorganic materials 0.000 title claims description 73
- 239000001569 carbon dioxide Substances 0.000 title claims description 73
- 230000009467 reduction Effects 0.000 title claims description 42
- 238000000034 method Methods 0.000 title claims description 21
- 239000003575 carbonaceous material Substances 0.000 claims description 65
- 239000000758 substrate Substances 0.000 claims description 48
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 45
- 229910052709 silver Inorganic materials 0.000 claims description 41
- 239000004332 silver Substances 0.000 claims description 41
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 38
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 37
- 229910002091 carbon monoxide Inorganic materials 0.000 claims description 37
- 239000002904 solvent Substances 0.000 claims description 33
- 229910052799 carbon Inorganic materials 0.000 claims description 26
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 25
- 238000004519 manufacturing process Methods 0.000 claims description 24
- 229910052751 metal Inorganic materials 0.000 claims description 22
- 239000002184 metal Substances 0.000 claims description 22
- 239000011941 photocatalyst Substances 0.000 claims description 20
- 229910052697 platinum Inorganic materials 0.000 claims description 19
- 229910021387 carbon allotrope Inorganic materials 0.000 claims description 15
- 239000010949 copper Substances 0.000 claims description 14
- 239000010931 gold Substances 0.000 claims description 12
- 239000003426 co-catalyst Substances 0.000 claims description 11
- 239000013078 crystal Substances 0.000 claims description 11
- 239000003014 ion exchange membrane Substances 0.000 claims description 10
- 239000002245 particle Substances 0.000 claims description 8
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 7
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 6
- 229910052796 boron Inorganic materials 0.000 claims description 6
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 6
- 229910052737 gold Inorganic materials 0.000 claims description 6
- 229910003460 diamond Inorganic materials 0.000 claims description 5
- 239000010432 diamond Substances 0.000 claims description 5
- 230000001678 irradiating effect Effects 0.000 claims description 4
- 230000003647 oxidation Effects 0.000 claims description 4
- 238000007254 oxidation reaction Methods 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 4
- 238000005245 sintering Methods 0.000 claims description 3
- 229910021645 metal ion Inorganic materials 0.000 claims description 2
- 238000006722 reduction reaction Methods 0.000 description 38
- 238000005868 electrolysis reaction Methods 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 238000000151 deposition Methods 0.000 description 5
- 238000004070 electrodeposition Methods 0.000 description 4
- 239000012528 membrane Substances 0.000 description 4
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 239000003792 electrolyte Substances 0.000 description 3
- 239000010944 silver (metal) Substances 0.000 description 3
- -1 silver ions Chemical class 0.000 description 3
- 229910001961 silver nitrate Inorganic materials 0.000 description 3
- 229910052938 sodium sulfate Inorganic materials 0.000 description 3
- 235000011152 sodium sulphate Nutrition 0.000 description 3
- 229920000557 Nafion® Polymers 0.000 description 2
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 2
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 2
- 230000005587 bubbling Effects 0.000 description 2
- 239000011203 carbon fibre reinforced carbon Substances 0.000 description 2
- 150000001768 cations Chemical class 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000000635 electron micrograph Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 238000006552 photochemical reaction Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 229910001415 sodium ion Inorganic materials 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- YZCKVEUIGOORGS-UHFFFAOYSA-N Hydrogen atom Chemical compound [H] YZCKVEUIGOORGS-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 150000001721 carbon Chemical class 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000005341 cation exchange Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010494 dissociation reaction Methods 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000010946 fine silver Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000004817 gas chromatography Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- GPRLSGONYQIRFK-UHFFFAOYSA-N hydron Chemical compound [H+] GPRLSGONYQIRFK-UHFFFAOYSA-N 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000006479 redox reaction Methods 0.000 description 1
- 230000027756 respiratory electron transport chain Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 239000011787 zinc oxide Substances 0.000 description 1
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- Electrodes For Compound Or Non-Metal Manufacture (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Carbon And Carbon Compounds (AREA)
- Catalysts (AREA)
Description
本発明は、二酸化炭素還元装置および還元方法に関し、特に、光触媒を用いた二酸化炭素還元に関する。 The present invention relates to a carbon dioxide reduction device and a reduction method, and more particularly to carbon dioxide reduction using a photocatalyst.
二酸化炭素還元方法としては、光触媒の存在の下、紫外線、太陽光などの光を照射して二酸化炭素を還元する方法が知られている（特許文献１参照）。そこでは、酸化チタン、酸化亜鉛などの光触媒の存在下において光を照射し、化学的反応によって二酸化炭素を固定化する。 As a carbon dioxide reduction method, there is known a method of reducing carbon dioxide by irradiating light such as ultraviolet rays or sunlight in the presence of a photocatalyst (see Patent Document 1). There, light is irradiated in the presence of a photocatalyst such as titanium oxide or zinc oxide to immobilize carbon dioxide by a chemical reaction.
また、ｓｐ3結晶構造である炭素同素体を含む炭素材を光触媒として利用することで、二酸化炭素を還元することが可能である（特許文献２参照）。二酸化炭素を溶解させた溶媒に設置されたプレート状の炭素材に紫外光を照射すると、高い光エネルギーによって光触媒が励起し、二酸化炭素が還元されてＣＯが生成される。 Further, carbon dioxide containing carbon allotrope having an sp 3 crystal structure can be used as a photocatalyst to reduce carbon dioxide (see Patent Document 2). When a plate-shaped carbon material placed in a solvent in which carbon dioxide is dissolved is irradiated with ultraviolet light, photocatalyst is excited by high light energy, carbon dioxide is reduced, and CO is generated.
光触媒を用いた二酸化炭素還元は、二酸化炭素をより多く還元できることが課題であり、炭素材を用いた二酸化炭素還元においても、さらなる還元効率の向上が求められる。 The problem with carbon dioxide reduction using a photocatalyst is that more carbon dioxide can be reduced, and further reduction of carbon dioxide using a carbon material requires further improvement in reduction efficiency.
本発明の二酸化炭素還元方法は、二酸化炭素を溶媒中に溶解させ、ｓｐ3結晶構造である炭素同素体を含むプレート状の炭素材を、光触媒として溶媒中に配する（配置する）。そして、炭素材に対し、炭素同素体を励起させる紫外光を照射するとともに、炭素材を電源の負極に接続して電圧を印加することにより、溶媒中の二酸化炭素を還元し、ＣＯ（一酸化炭素）を生成する。 In the carbon dioxide reduction method of the present invention, carbon dioxide is dissolved in a solvent, and a plate-shaped carbon material containing a carbon allotrope having an sp 3 crystal structure is placed (disposed) in the solvent as a photocatalyst. Then, the carbon material is irradiated with ultraviolet light that excites the carbon allotrope, and the carbon material is connected to a negative electrode of a power source to apply a voltage to reduce carbon dioxide in the solvent, thereby reducing CO (carbon monoxide). ) Is generated.
本発明では、通常の電気分解ではＣＯを生成する二酸化炭素還元反応が生じない炭素材に対し、紫外光によって炭素同素体が励起した状態で負の電圧を印加することにより、ＣＯ生成量が増加することを初めて見出し、炭素材を光触媒として使用し、かつ電気分解のカソードとして機能させることでＣＯ生成に有効であることを導き出した。 In the present invention, the amount of CO produced is increased by applying a negative voltage to the carbon material in which carbon dioxide reduction reaction that produces CO is not generated by ordinary electrolysis while the carbon allotrope is excited by ultraviolet light. It was discovered for the first time that carbon materials were used as photocatalysts and functioned as cathodes for electrolysis, and were effective for CO production.
さらに本発明では、ｓｐ3結晶構造である炭素同素体を含む炭素材の表面に対し、金（Ａｕ）、銀（Ａｇ）、銅（Ｃｕ）、白金（Ｐｔ）の少なくともいずれか１つの金属を含む助触媒を担持させることにより、光触媒を用いたＣＯ生成においてＣＯ生成量の顕著な増加を実現できることを見出した。例えば人工ダイヤモンドから成る光触媒としての炭素材に対し、このような助触媒を担持させることで極めて有効にＣＯを生成することができる。助触媒としては、例えば銀から成る助触媒を用いることが可能である。 Furthermore, in the present invention, at least one metal of gold (Au), silver (Ag), copper (Cu), and platinum (Pt) is contained on the surface of the carbon material containing the carbon allotrope having the sp 3 crystal structure. It has been found that by supporting a cocatalyst, a remarkable increase in CO production amount can be realized in CO production using a photocatalyst. For example, CO can be generated very effectively by supporting such a promoter on a carbon material as a photocatalyst made of artificial diamond. As the co-catalyst, for example, a co-catalyst made of silver can be used.
プレート状の炭素材は、一体的な固体炭素であればよく、形状も典型的な薄板形状に限定されず、長手方向に延在するものであればよい。例えば炭素材は、ホウ素の重量濃度０．０１％〜４％のボロンドープダイヤモンド構造を有する基板で構成することが可能である。紫外光の波長は、２００ｎｍ〜２６０ｎｍの範囲に定めるのがよい。 The plate-shaped carbon material may be solid carbon solid, and the shape thereof is not limited to a typical thin plate shape, and any material extending in the longitudinal direction may be used. For example, the carbon material can be composed of a substrate having a boron-doped diamond structure with a boron concentration of 0.01% to 4%. The wavelength of ultraviolet light is preferably set in the range of 200 nm to 260 nm.
電解槽を構成する場合、炭素材の対極としてアノードを溶媒中に配し、電源の正極に接続して電圧を印加すればよい。また、炭素材とアノードとの間に、イオン交換膜を配置することも可能である。例えば、バブリングで二酸化炭素を溶解させる場合、二酸化炭素を炭素材傍に留めるため、気泡発生器を還元槽に配置することができる。 When configuring an electrolytic cell, an anode may be placed in a solvent as a counter electrode of a carbon material, connected to a positive electrode of a power source, and a voltage may be applied. It is also possible to dispose an ion exchange membrane between the carbon material and the anode. For example, when carbon dioxide is dissolved by bubbling, the bubble generator can be arranged in the reduction tank in order to keep the carbon dioxide near the carbon material.
例えば、紫外光が直接炭素材表面に照射されるようにするため、助触媒を、炭素材の表面において、粒子状になって散在するように担持させてもよい。すなわち、助触媒が表面を全体的に覆うのではなく、互いに離散的になって分散し、隙間が生じるように担持させればよい。 For example, in order to directly irradiate the surface of the carbon material with ultraviolet light, the promoter may be supported so as to be dispersed in the form of particles on the surface of the carbon material. In other words, the co-catalyst does not cover the entire surface, but may be dispersed so that the co-catalyst is dispersed and dispersed so that a gap is formed.
本発明の二酸化炭素還元装置は、容器と、容器に収容され、二酸化炭素の溶解した溶媒と、容器内に配置され、ｓｐ3結晶構造である炭素同素体を含むプレート状の炭素材と、炭素同素体を励起させる紫外光を、炭素材に照射する光源と、炭素材と負極において接続し、電圧を印加する給電装置と、容器内に配置され、給電装置の正極と接続するアノードとを備え、炭素材が、金（Ａｕ）、銀（Ａｇ）、銅（Ｃｕ）、白金（Ｐｔ）の少なくともいずれか１つの金属を含む助触媒を、その表面に担持している。 The carbon dioxide reduction device of the present invention includes a container, a solvent in which carbon dioxide is dissolved, a plate-shaped carbon material which is disposed in the container and includes a carbon allotrope having an sp 3 crystal structure, and a carbon allotrope. UV light for exciting the carbon material, a light source for irradiating the carbon material, a power supply device that is connected to the carbon material at the negative electrode and applies a voltage, and an anode that is arranged in the container and connected to the positive electrode of the power supply device. The material has on its surface a co-catalyst containing at least one metal of gold (Au), silver (Ag), copper (Cu), and platinum (Pt).
本発明の他の態様における炭素基板の製造方法は、二酸化炭素還元装置の溶媒中に光触媒として配置される炭素基板の製造方法であって、金属イオンが溶解した溶液中で炭素基板に還元電流を流し、粒子状になって散在するように金属を基板上に析出させ、金属が析出した炭素基板を、金属の酸化を抑制するように焼結する製造方法であって、金属が、金（Ａｕ）、銀（Ａｇ）、銅（Ｃｕ）、白金（Ｐｔ）の少なくともいずれか１つを含む。 A method for producing a carbon substrate in another aspect of the present invention is a method for producing a carbon substrate arranged as a photocatalyst in a solvent of a carbon dioxide reduction device, wherein a reducing current is applied to the carbon substrate in a solution in which metal ions are dissolved. It is a manufacturing method in which a metal is deposited on a substrate so as to be scattered in the form of particles and scattered, and a carbon substrate on which the metal is deposited is sintered so as to suppress oxidation of the metal. ), silver (Ag), copper (Cu), and platinum (Pt).
本発明によれば、二酸化炭素還元装置において、二酸化炭素を効率よく還元することができる。 According to the present invention, carbon dioxide can be efficiently reduced in a carbon dioxide reduction device.
以下では、図面を参照して本発明の実施形態について説明する。 Embodiments of the present invention will be described below with reference to the drawings.
図１は、本実施形態である二酸化炭素還元装置を模式的に示した図である。図２は、炭素材の表面の電子顕微鏡写真を示した図である。 FIG. 1 is a diagram schematically showing a carbon dioxide reduction device according to this embodiment. FIG. 2 is a view showing an electron micrograph of the surface of the carbon material.
二酸化炭素還元装置１０は、容器１５、気泡発生器１７、炭素材２０、光源ユニット３５、二酸化炭素供給器５０、および循環ポンプ（図示せず）を備え、容器１５には溶媒４０が収容されている。二酸化炭素供給器５０は、配管２５を介して二酸化炭素を気泡発生器１７へ送り込む。 The carbon dioxide reduction device 10 includes a container 15, a bubble generator 17, a carbon material 20, a light source unit 35, a carbon dioxide supplier 50, and a circulation pump (not shown), and the container 15 contains a solvent 40. There is. The carbon dioxide supplier 50 sends carbon dioxide to the bubble generator 17 through the pipe 25.
光源ユニット３５のランプ３０は、２００ｎｍ〜２６０ｎｍの波長をもつ紫外光を放射する長尺管状の紫外線ランプ（例えば、エキシマランプ）であり、溶媒４０の液面下に入れて容器深さ方向に沿って配置される。ランプ３０は、ガラス管などの管状保護部材３２に収容されており、溶媒４０とランプ３０との間には、溶媒４０が入り込まない密閉空間が形成されている。 The lamp 30 of the light source unit 35 is a long tubular ultraviolet lamp (for example, an excimer lamp) that emits ultraviolet light having a wavelength of 200 nm to 260 nm, and is placed below the liquid surface of the solvent 40 to extend in the depth direction of the container. Are arranged. The lamp 30 is housed in a tubular protection member 32 such as a glass tube, and a sealed space in which the solvent 40 does not enter is formed between the solvent 40 and the lamp 30.
電解を行うための溶媒４０として、可溶な電解質を溶解した水溶液を用いることが可能であり、あるいは、有機溶液、イオン性溶媒なども適用可能である。ここでは、硫酸ナトリウム水溶液が溶媒４０として用いられている。溶媒４０に対する二酸化炭素の溶解は、バブリングによって行われる。 As the solvent 40 for electrolysis, an aqueous solution in which a soluble electrolyte is dissolved can be used, or an organic solution, an ionic solvent, or the like can be applied. Here, an aqueous solution of sodium sulfate is used as the solvent 40. The carbon dioxide is dissolved in the solvent 40 by bubbling.
光触媒として用いられる炭素材２０は、容器深さ方向に延びる一枚のプレート状に形成された固体炭素（以下、炭素基板ともいう）によって成形されている。作用極となる炭素基板２０は、ｓｐ3結晶構造の炭素同素体から成り、例えばホウ素の重量濃度０．０１〜４．０％のボロンドープダイヤモンド（ＢＤＤ）によって構成される。 The carbon material 20 used as a photocatalyst is formed by solid carbon (hereinafter also referred to as a carbon substrate) formed in a plate shape extending in the depth direction of the container. The carbon substrate 20 serving as the working electrode is made of a carbon allotrope having an sp 3 crystal structure, and is made of, for example, boron-doped diamond (BDD) having a boron weight concentration of 0.01 to 4.0%.
溶媒４０中には、炭素材２０に加え、導電性の金属板２１が配されている。電源（給電装置）３６は、炭素材２０、金属板２１と接続されており、炭素材２０は負極に、金属板２１は正極に接続されている。ここでは、金属板２１は白金基板（以下、白金電極ともいう）によって構成されている。 In the solvent 40, a conductive metal plate 21 is arranged in addition to the carbon material 20. The power supply (power supply device) 36 is connected to the carbon material 20 and the metal plate 21, the carbon material 20 is connected to the negative electrode, and the metal plate 21 is connected to the positive electrode. Here, the metal plate 21 is composed of a platinum substrate (hereinafter also referred to as a platinum electrode).
炭素材２０と金属板２１との間には、イオン交換膜６０が配置されている。イオン交換膜６０は、陽イオンのみを透過させる陽イオン交換膜によって構成されている。イオン交換膜６０によって、炭素材２０の配置された還元槽と、金属板２１の配置された酸化槽とが、溶媒４０において区画される。 An ion exchange membrane 60 is arranged between the carbon material 20 and the metal plate 21. The ion exchange membrane 60 is composed of a cation exchange membrane that allows only cations to pass through. The ion exchange membrane 60 divides the reducing tank in which the carbon material 20 is arranged and the oxidizing tank in which the metal plate 21 is arranged in the solvent 40.
炭素基板２０の基板表面２０Ｓには、銀が助触媒として担持されている。図２に示すように、基板表面２０Ｓにおいて銀粒子が離散的になっていて散在しており、粒径が１０ｎｍ〜１００ｎｍ程度の微細な銀粒子で構成されている。このような基板表面２０Ｓ上へ銀を担持させた炭素基板２０を製造するため、銀の析出、焼結を行う。 Silver is supported as a co-catalyst on the substrate surface 20S of the carbon substrate 20. As shown in FIG. 2, silver particles are dispersed and scattered on the substrate surface 20S, and are composed of fine silver particles having a particle size of about 10 nm to 100 nm. In order to manufacture the carbon substrate 20 supporting silver on the substrate surface 20S, silver deposition and sintering are performed.
基板表面２０Ｓ上への銀の析出方法としては、ここでは電着法を用いている。具体的には、硝酸銀水溶液中で炭素基板２０に還元電流を流すことによって、銀イオンが電解還元されると同時に基板表面２０Ｓ上に銀が析出される。銀の析出後、銀を固定するために炭素基板２０が焼結される。このとき、銀の酸化を抑えるように焼結が行われる。ここでは、水素雰囲気下で所定温度、所定時間の加熱を行う。銀の担持量および図２に示した銀の粒子状、離散的分布の程度（密度）は、硝酸銀水溶液の濃度、還元電流量、通電時間などを調整することによって制御することができる。 As a method for depositing silver on the substrate surface 20S, an electrodeposition method is used here. Specifically, by applying a reducing current to the carbon substrate 20 in an aqueous silver nitrate solution, silver ions are electrolytically reduced and at the same time silver is deposited on the substrate surface 20S. After silver deposition, the carbon substrate 20 is sintered to fix the silver. At this time, sintering is performed so as to suppress silver oxidation. Here, heating is performed in a hydrogen atmosphere at a predetermined temperature for a predetermined time. The amount of silver supported and the degree of silver particle shape and discrete distribution (density) shown in FIG. 2 can be controlled by adjusting the concentration of the silver nitrate aqueous solution, the reduction current amount, the energization time, and the like.
このような二酸化炭素還元装置１０において、以下の動作を行うことによって二酸化炭素が還元される。循環ポンプを作動させることにより、気泡発生器１７によって気泡が生じ、二酸化炭素が溶媒４０に溶解する。二酸化炭素が溶解した状態で、光源用電源（図示せず）からランプ３０に対して電力を供給すると同時に、電源３６によって炭素材２０、白金基板２１に対して電圧をかける。炭素材２０には負の電圧、白金基板２１には正の電圧が印加される。 In such a carbon dioxide reduction device 10, carbon dioxide is reduced by performing the following operations. By operating the circulation pump, bubbles are generated by the bubble generator 17, and carbon dioxide is dissolved in the solvent 40. In a state where carbon dioxide is dissolved, electric power is supplied from a light source power source (not shown) to the lamp 30, and at the same time, a voltage is applied to the carbon material 20 and the platinum substrate 21 by the power source 36. A negative voltage is applied to the carbon material 20, and a positive voltage is applied to the platinum substrate 21.
ランプ３０から放射された紫外光が炭素材２０に照射されると、ｓｐ3結晶構造の炭素同素体が励起し、電子が放出される。この電子放出に伴って生じる比較的高い光エネルギーが二酸化炭素（ＣＯ2）のＣ＝Ｏ結合を切り離し、一酸化炭素（ＣＯ）が生成される。生成された一酸化炭素は、気相中に放出される。 When the carbon material 20 is irradiated with the ultraviolet light emitted from the lamp 30, the carbon allotrope of the sp 3 crystal structure is excited and electrons are emitted. The relatively high light energy that accompanies this electron emission cleaves the C═O bond of carbon dioxide (CO 2 ) to produce carbon monoxide (CO). The carbon monoxide produced is released into the gas phase.
２ＣＯ2→２ＣＯ＋Ｏ2 2CO 2 → 2CO+O 2
一方、電解質の溶媒４０に入れた炭素材２０と金属板２１に対して所定電圧が印加されることにより、ＣＯを生成する二酸化炭素還元反応が生じる。このＣＯ生成の二酸化炭素還元反応は、光触媒に基づく還元反応（光化学反応）が生じている状態でしか実質的に生じない。 On the other hand, when a predetermined voltage is applied to the carbon material 20 and the metal plate 21 contained in the electrolyte solvent 40, a carbon dioxide reduction reaction that produces CO occurs. This carbon dioxide reduction reaction of CO generation substantially occurs only in the state where the reduction reaction (photochemical reaction) based on the photocatalyst is occurring.
つまり、炭素材２０と白金基板２１とをそれぞれカソード（陰極）、アノード（陽極）として酸化還元反応を生じさせる電気分解を行っても、紫外光によってｓｐ3結晶構造の炭素同素体が励起していなければ、ＣＯ生成の二酸化炭素還元反応は生じない。ここでの電気分解は、あくまでも光触媒の存在下でＣＯ生成を促進させる付随的な化学処理といえる。炭素材２０に印加する負の電圧は、ＣＯ生成の二酸化炭素還元反応が効果的に生じる電圧に設定すればよく、（マイナス）数ボルト程度でよい。 That is, even when electrolysis is performed by using the carbon material 20 and the platinum substrate 21 as a cathode (cathode) and an anode (anode) to cause a redox reaction, the carbon allotrope of the sp 3 crystal structure must be excited by the ultraviolet light. Thus, the carbon dioxide reduction reaction of CO production does not occur. Electrolysis here can be said to be an incidental chemical treatment that promotes CO production in the presence of a photocatalyst. The negative voltage applied to the carbon material 20 may be set to a voltage at which the carbon dioxide reduction reaction of CO generation effectively occurs, and may be about (minus) several volts.
イオン交換膜６０は、例えば、ナフィオン膜（登録商標）が適用可能である。電解質の解離と電気分解によって硫酸イオン（Ｓ2Ｏ4 2-）、ナトリウムイオン（Ｎａ+）、水素イオン（Ｈ+）などが生成されるが、ナトリウムイオン、水素イオンなどの陽イオンのみイオン交換膜６０を通過することができる。 As the ion exchange membrane 60, for example, a Nafion membrane (registered trademark) can be applied. Sulfate ion (S 2 O 4 2 - ), sodium ion (Na + ) and hydrogen ion (H + ) are generated by dissociation and electrolysis of the electrolyte, but only cations such as sodium ion and hydrogen ion are ion-exchanged. It can pass through the membrane 60.
また、陰イオンとともに、溶媒４０中に溶解された二酸化炭素、そして二酸化炭素から生成される炭酸イオン（ＣＯ3 2-など）も、イオン交換膜６０を通過することができない。これにより、還元槽に設置された気泡発生器１７によって溶媒４０中に溶解した二酸化炭素が還元槽に留められることになり、ＣＯ生成が促進される。 In addition to the anions, carbon dioxide dissolved in the solvent 40 and carbonate ions (CO 3 2− etc.) generated from the carbon dioxide cannot pass through the ion exchange membrane 60. As a result, carbon dioxide dissolved in the solvent 40 is retained in the reducing tank by the bubble generator 17 installed in the reducing tank, and CO production is promoted.
さらに、助触媒として炭素基板２０に銀を担持させることにより、二酸化炭素が銀に吸着し、吸着した二酸化炭素に対して電子を供給することで、二酸化炭素の還元がより促進される。特に、銀イオンの電解還元を利用する電着法によって銀を析出させたことにより、炭素基板２０の電子の移動箇所に銀が析出され、吸着した二酸化炭素に電子を効率よく供給することができる。また、基板表面２０Ｓ全体を銀で覆うのではなく、粒子状の銀を散在させている（離散的な分布にしている）ため、紫外光が炭素基板２０の基板表面２０Ｓを直接照射し、炭素基板２０が励起されて二酸化炭素還元に寄与する。 Furthermore, by supporting silver on the carbon substrate 20 as a co-catalyst, carbon dioxide is adsorbed on silver and electrons are supplied to the adsorbed carbon dioxide, whereby the reduction of carbon dioxide is further promoted. In particular, by depositing silver by the electrodeposition method utilizing electrolytic reduction of silver ions, silver is deposited at the electron transfer position of the carbon substrate 20, and the electrons can be efficiently supplied to the adsorbed carbon dioxide. .. Further, since the particulate silver is scattered (having a discrete distribution) instead of covering the entire substrate surface 20S with silver, the ultraviolet light directly irradiates the substrate surface 20S of the carbon substrate 20, and carbon The substrate 20 is excited and contributes to carbon dioxide reduction.
このように本実施形態によれば、二酸化炭素還元装置１０において、光源ユニット３５、ｓｐ3結晶構造の炭素同素体から成るとともに、銀を基板表面２０Ｓに担持させたプレート状炭素材／炭素基板２０を、二酸化炭素の溶解した溶媒４０中に配置する。さらに、炭素材２０とともに白金基板２１を溶媒４０中に配置し、炭素材２０、白金基板２１をそれぞれ電源３６の負極、正極に接続する。そして、ランプ３０から紫外光を炭素材２０に向けて照射するとともに、炭素材２０、白金基板２１に対して電圧を印加する。光触媒であって助触媒として銀を担持させた炭素材２０に対し、紫外光照射とともに電圧印加を行うことにより、ＣＯが効果的に生成される。 As described above, according to the present embodiment, in the carbon dioxide reduction device 10, the plate-shaped carbon material/carbon substrate 20 that includes the light source unit 35 and the carbon allotrope of the sp 3 crystal structure and has silver supported on the substrate surface 20S. , Placed in a solvent 40 in which carbon dioxide is dissolved. Furthermore, the platinum substrate 21 is placed in the solvent 40 together with the carbon material 20, and the carbon material 20 and the platinum substrate 21 are connected to the negative electrode and the positive electrode of the power source 36, respectively. Then, while irradiating the carbon material 20 with ultraviolet light from the lamp 30, a voltage is applied to the carbon material 20 and the platinum substrate 21. CO is effectively generated by applying a voltage to the carbon material 20 which is a photocatalyst and supports silver as a co-catalyst together with ultraviolet light irradiation.
なお、白金基板以外のアノードを炭素材の対極として設置してもよい。あるいは、炭素材のみを設置し、負の電圧を印加するように構成してもよい。 An anode other than the platinum substrate may be installed as a counter electrode of the carbon material. Alternatively, only the carbon material may be installed and a negative voltage may be applied.
銀の析出については、硝酸銀水溶液以外でもよく、銀イオンが溶解した溶液を用いてもよい。また、電着法の代わりに含侵法、光吸着法を用いて銀を析出してもよい。 For the deposition of silver, a solution other than an aqueous solution of silver nitrate may be used, or a solution in which silver ions are dissolved may be used. Further, instead of the electrodeposition method, the impregnation method or the photoadsorption method may be used to deposit silver.
銀以外の金属を助触媒として用いることが可能であり、同様な触媒作用のある金（Ａｕ）、銅（Ｃｕ）、白金（Ｐｔ）を担持させてもよく、あるいは銀を含めてそれらの組合せであってもよい。すなわち、これらの金属は、イオン化したときのイオン価数が同じもしくは同等であって電子の軌道としてｄ軌道あるいはｆ軌道をもち、周期表において遷移元素の中で互いに隣接する金属であり、銀と同様にＣＯ生成量の増加を得ることができる。 A metal other than silver can be used as a co-catalyst, and gold (Au), copper (Cu), platinum (Pt) having similar catalytic action may be supported, or a combination thereof including silver. May be That is, these metals are metals that have the same or equivalent ionic valences when they are ionized, have a d orbit orbit as an electron orbit, and are adjacent to each other among transition elements in the periodic table. Similarly, an increase in CO production can be obtained.
以下、実施例を用いて、光触媒に対する光照射および電圧印加の同時プロセスの有効性および炭素材に銀担持させたときの有効性について説明する。まず実施例１において、光触媒に対する光照射および電圧印加の同時プロセスの有効性を説明し、実施例２において、銀担持の有効性を説明する。 Hereinafter, the effectiveness of the simultaneous process of light irradiation and voltage application to the photocatalyst and the effectiveness when silver is supported on the carbon material will be described using examples. First, the effectiveness of the simultaneous process of light irradiation and voltage application to the photocatalyst will be described in Example 1, and the effectiveness of silver loading will be described in Example 2.
実施例１である二酸化炭素還元装置は、本実施形態に対応する装置であるが、炭素材表面に対して銀を担持させていない。炭素材は、ホウ素の重量濃度０．１％をドープさせたＢＤＤ基板によって構成される。また、溶媒は、硫酸ナトリウム水溶液で構成される。酸化槽と還元槽とを区画するイオン交換膜にはナフィオン膜（登録商標）が用いられている。ランプは、波長２２２ｎｍの紫外光を照射するエキシマランプによって構成される。 The carbon dioxide reduction device of Example 1 is a device corresponding to this embodiment, but silver is not supported on the surface of the carbon material. The carbon material is composed of a BDD substrate doped with 0.1% by weight of boron. Further, the solvent is composed of an aqueous solution of sodium sulfate. A Nafion membrane (registered trademark) is used as an ion exchange membrane that divides the oxidation tank and the reduction tank. The lamp is composed of an excimer lamp that emits ultraviolet light having a wavelength of 222 nm.
このような二酸化炭素還元装置に対し、条件を変えながら二酸化炭素還元によるＣＯ生成量を時間経過とともに測定した。具体的には、紫外光照射しなかった場合と、紫外光照射のみ行った場合と、紫外光照射と電圧印加との両方を行った場合について、ＣＯ生成量を測定した。実験では、ＣＯ2を溶媒４０が１．４ｇ／ｌ濃度となるようにバブリングし、ＢＤＤ基板に対し−１．８Ｖ、白金電極に対して＋１．８Ｖの電圧を印加した。また、ＣＯ生成量の測定は、ガスクロマトグラフィによって行った。 With respect to such a carbon dioxide reduction device, the CO production amount by carbon dioxide reduction was measured over time while changing the conditions. Specifically, the CO production amount was measured in the case where the ultraviolet light irradiation was not performed, the case where only the ultraviolet light irradiation was performed, and the case where both the ultraviolet light irradiation and the voltage application were performed. In the experiment, CO 2 was bubbled so that the concentration of the solvent 40 was 1.4 g/l, and a voltage of −1.8 V was applied to the BDD substrate and a voltage of +1.8 V was applied to the platinum electrode. The CO production amount was measured by gas chromatography.
図３は、ＣＯ生成量（μｍｏｌ）を示したグラフである。図３に示すように、電圧印加だけではＣＯ生成が生じていないことが明らかになっている。これは、ＢＤＤ基板のような炭素材をカソードとして用いた電気分解を行っても、ＣＯ生成の還元反応が生じないことを示している。 FIG. 3 is a graph showing the CO production amount (μmol). As shown in FIG. 3, it has been clarified that CO is not generated only by applying the voltage. This indicates that even if electrolysis is performed using a carbon material such as a BDD substrate as a cathode, a reduction reaction of CO generation does not occur.
一方、炭素材に対する紫外光照射と電圧印加との両方の処理によって、ＣＯ生成量が著しく増加した。励起されたｓｐ3結晶構造の炭素材へ電圧を印加することが光触媒の存在下のＣＯ生成（光化学反応）を促進させることが証明されている。 On the other hand, the CO production amount was remarkably increased by both the irradiation of the carbon material with the ultraviolet light and the voltage application. It has been proved that applying a voltage to an excited carbon material having an sp 3 crystal structure promotes CO production (photochemical reaction) in the presence of a photocatalyst.
実施例２である二酸化炭素還元装置は、炭素材に銀を助触媒として担持させており、電着法により銀を担持したホウ素の重量濃度０．１％をドープさせたＢＤＤ基板によって構成される。この炭素基板を、２５ｍｏｌ／ｌ硫酸ナトリウム溶液中に配置し、対極には白金電極をイオン交換膜で区切られた溶液槽に配置した。そして炭素基板に−１．６Ｖの電圧を印加し、エキシマランプによって波長２２２ｎｍの紫外光を照射した。 The carbon dioxide reduction apparatus according to Example 2 has a carbon material supporting silver as a co-catalyst, and is constituted by a BDD substrate doped with 0.1% by weight concentration of boron carrying silver by an electrodeposition method. .. This carbon substrate was placed in a 25 mol/l sodium sulfate solution, and a platinum electrode was placed as a counter electrode in a solution tank partitioned by an ion exchange membrane. Then, a voltage of -1.6 V was applied to the carbon substrate, and ultraviolet light having a wavelength of 222 nm was irradiated by an excimer lamp.
図４は、実施例２の二酸化炭素還元装置のＣＯ生成量と、銀を担持していない実施例１の二酸化炭素還元装置のＣＯ生成量とを示したグラフである。ただし、印加電圧などの実験条件は実施例２の条件に揃えている。図４から明らかなように、銀を炭素基板に担持させることで、ＣＯ生成量が顕著に増加する。 FIG. 4 is a graph showing the CO production amount of the carbon dioxide reduction device of Example 2 and the CO production amount of the carbon dioxide reduction device of Example 1 which does not carry silver. However, the experimental conditions such as applied voltage are the same as those of the second embodiment. As is clear from FIG. 4, the amount of CO produced is remarkably increased by supporting silver on the carbon substrate.
１０ 二酸化炭素還元装置
１５ 容器
１７ 気泡発生器
２０ 炭素材／炭素基板（カソード）
２０Ｓ 基板表面
２１ 金属板／白金基板（アノード）
３０ ランプ
３５ 光源ユニット
３６ 電源
４０ 溶媒
５０ 二酸化炭素供給器
６０ イオン交換膜
10 Carbon Dioxide Reduction Device 15 Container 17 Bubble Generator 20 Carbon Material/Carbon Substrate (Cathode)
20S substrate surface 21 metal plate/platinum substrate (anode)
30 Lamp 35 Light Source Unit 36 Power Supply 40 Solvent 50 Carbon Dioxide Feeder 60 Ion Exchange Membrane
Claims (10)
ｓｐ3結晶構造である炭素同素体を含むプレート状の炭素材であって、その表面に対し、金（Ａｕ）、銀（Ａｇ）、銅（Ｃｕ）、白金（Ｐｔ）の少なくともいずれか１つの金属を含む助触媒を担持させた炭素材を、光触媒として前記溶媒中に配し、
前記助触媒が、前記炭素材の表面において、粒子状になって散在し、
前記炭素材に対し、前記炭素同素体を励起させる紫外光を照射するとともに、前記炭素材を電源の負極に接続して電圧を印加することにより、前記溶媒中の二酸化炭素を還元し、一酸化炭素を生成することを特徴とする二酸化炭素還元方法。 Dissolve carbon dioxide in the solvent,
A plate-shaped carbon material containing a carbon allotrope having an sp 3 crystal structure, and at least one metal of gold (Au), silver (Ag), copper (Cu), and platinum (Pt) on the surface thereof. A carbon material supporting a co-catalyst containing is placed in the solvent as a photocatalyst,
The promoter is dispersed in the form of particles on the surface of the carbon material,
The carbon material is irradiated with ultraviolet light that excites the carbon allotrope, and the carbon material is connected to a negative electrode of a power source to apply a voltage to reduce carbon dioxide in the solvent and carbon monoxide. A method for reducing carbon dioxide, which comprises:
前記容器に収容され、二酸化炭素の溶解した溶媒と、
前記容器内に配置され、ｓｐ3結晶構造である炭素同素体を含むプレート状の炭素材と、
前記炭素同素体を励起させる紫外光を、前記炭素材に照射する光源と、
前記炭素材と負極において接続し、電圧を印加する給電装置と、
前記容器内に収容された前記溶媒中に配置され、前記給電装置の正極と接続するアノードとを備え、
前記炭素材の表面には、金（Ａｕ）、銀（Ａｇ）、銅（Ｃｕ）、白金（Ｐｔ）の少なくともいずれか１つの金属を含む助触媒を担持していることを特徴とする二酸化炭素還元装置。 A container,
Stored in the container, a solvent in which carbon dioxide is dissolved,
A plate-shaped carbon material arranged in the container, containing a carbon allotrope having an sp 3 crystal structure,
Ultraviolet light for exciting the carbon allotrope, a light source for irradiating the carbon material,
A power supply device that is connected to the carbon material at the negative electrode and applies a voltage,
Disposed in the solvent contained in the container, comprising an anode connected to the positive electrode of the power supply device,
Carbon dioxide characterized in that a cocatalyst containing at least one metal of gold (Au), silver (Ag), copper (Cu), and platinum (Pt) is carried on the surface of the carbon material. Reduction device.
金属イオンが溶解した溶液中で炭素基板に還元電流を流し、粒子状になって散在するように金属を基板上に析出させ、
前記金属が析出した炭素基板を、前記金属の酸化を抑制するように焼結する製造方法であって、
前記金属が、金（Ａｕ）、銀（Ａｇ）、銅（Ｃｕ）、白金（Ｐｔ）の少なくともいずれか１つを含むことを特徴とする炭素基板の製造方法。
A method for producing a carbon substrate arranged as a photocatalyst in a solvent of a carbon dioxide reduction device,
A reducing current is applied to the carbon substrate in a solution in which metal ions are dissolved, and the metal is deposited on the substrate so as to be dispersed in the form of particles,
A manufacturing method of sintering a carbon substrate on which the metal is deposited so as to suppress oxidation of the metal,
The method for producing a carbon substrate, wherein the metal contains at least one of gold (Au), silver (Ag), copper (Cu), and platinum (Pt).
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