JP2018016535A - Carbon dioxide reduction device and reduction method - Google Patents

Carbon dioxide reduction device and reduction method Download PDF

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JP2018016535A
JP2018016535A JP2016150546A JP2016150546A JP2018016535A JP 2018016535 A JP2018016535 A JP 2018016535A JP 2016150546 A JP2016150546 A JP 2016150546A JP 2016150546 A JP2016150546 A JP 2016150546A JP 2018016535 A JP2018016535 A JP 2018016535A
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carbon
carbon dioxide
carbon material
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JP6713121B2 (en
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千晶 寺島
Chiaki Terajima
千晶 寺島
裕衣里 平野
Yuiri Hirano
裕衣里 平野
ニティッシュ ロイ
Nitish Roy
ニティッシュ ロイ
孝宗 鈴木
Takamune Suzuki
孝宗 鈴木
一弥 中田
Kazuya Nakata
一弥 中田
勝又 健一
Kenichi Katsumata
健一 勝又
藤嶋 昭
Akira Fujishima
昭 藤嶋
湯浅 真
Makoto Yuasa
真 湯浅
近藤 剛史
Takashi Kondo
剛史 近藤
晴男 栗山
Haruo Kuriyama
晴男 栗山
芹澤 和泉
Izumi Serizawa
和泉 芹澤
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Orc Manufacturing Co Ltd
Tokyo University of Science
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Orc Manufacturing Co Ltd
Tokyo University of Science
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Abstract

PROBLEM TO BE SOLVED: To effectively reduce carbon dioxide by a carbon dioxide reduction device.SOLUTION: A light source unit 35 and a plate-shaped carbon material/carbon substrate 20 consisting of carbon allotrope with a spcrystal structure and having silver carried on a substrate surface 20S are arranged in a solvent 40 by dissolving carbon dioxide in a carbon dioxide reduction device 10. Further, a platinum substrate 21 together with the carbon material 20 is arranged in a container 15, the carbon material 20 and the platinum substrate 21 are connected to an anode and a cathode of an electric power source 36, respectively. The carbon material 20 is irradiated with ultraviolet light from a lamp 30 and electric voltage is applied to the carbon material 20 and the platinum substrate 21.SELECTED DRAWING: Figure 1

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, a method of reducing carbon dioxide by irradiating light such as ultraviolet rays or sunlight in the presence of a photocatalyst is known (see Patent Document 1). There, light is irradiated in the presence of a photocatalyst such as titanium oxide or zinc oxide, and carbon dioxide is immobilized 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。 In addition, carbon dioxide can be reduced by using a carbon material containing a carbon allotrope having an sp 3 crystal structure as a photocatalyst (see Patent Document 2). When a plate-like carbon material placed in a solvent in which carbon dioxide is dissolved is irradiated with ultraviolet light, the photocatalyst is excited by high light energy, and carbon dioxide is reduced to produce CO.

特開2009−62321号公報JP 2009-62321 A 特開2015−151285号公報JP2015-151285A

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。   Carbon dioxide reduction using a photocatalyst is a problem that more carbon dioxide can be reduced, and further improvement in reduction efficiency is required in carbon dioxide reduction using a carbon material.

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-like carbon material containing a carbon allotrope having an sp 3 crystal structure is arranged (arranged) 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 the negative electrode of the power source to apply a voltage, thereby reducing carbon dioxide in the solvent, and 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 generated is increased by applying a negative voltage to a carbon material that does not undergo a carbon dioxide reduction reaction that generates CO in normal electrolysis while the carbon allotrope is excited by ultraviolet light. It was found for the first time that carbon material was used as a photocatalyst and it was effective for CO production by functioning as a cathode for electrolysis.

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, the surface of the carbon material containing the carbon allotrope having the sp 3 crystal structure contains at least one of gold (Au), silver (Ag), copper (Cu), and platinum (Pt). It has been found that a significant increase in the amount of CO produced in CO production using a photocatalyst can be realized by supporting a cocatalyst. 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 promoter, for example, a promoter 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-like carbon material may be an integral solid carbon, and the shape is not limited to a typical thin plate shape, and may be any material that extends in the longitudinal direction. For example, the carbon material can be composed of a substrate having a boron-doped diamond structure with a boron weight concentration of 0.01% to 4%. The wavelength of the 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 the carbon material, and a voltage may be applied by connecting to the positive electrode of the power source. 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, a bubble generator can be placed in the reduction tank 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 scattered in the form of particles on the surface of the carbon material. That is, the cocatalyst does not cover the entire surface, but may be supported so as to be dispersed and dispersed to form a gap.

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 apparatus of the present invention includes a container, a solvent in which the carbon dioxide is dissolved, a plate-like carbon material that is disposed in the container and includes a carbon allotrope having an sp 3 crystal structure, and a carbon allotrope A light source that irradiates the carbon material with ultraviolet light that excites the carbon material, a power supply device that connects the carbon material and the negative electrode and applies a voltage, and an anode that is disposed in the container and is connected to the positive electrode of the power supply device. The material carries on its surface a promoter containing at least one 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 that is arranged as a photocatalyst in a solvent of a carbon dioxide reduction device, and a reduction current is applied to the carbon substrate in a solution in which metal ions are dissolved. A manufacturing method in which a metal is deposited on a substrate so as to be scattered and dispersed in a particulate form, 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.

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。It is the figure which showed typically the carbon dioxide reduction apparatus which is this embodiment. 炭素材の表面の電子顕微鏡写真を示した図である。It is the figure which showed the electron micrograph of the surface of a carbon material. 実施例1である二酸化炭素還元装置のCO生成量の比較グラフである。3 is a comparative graph of the amount of CO produced by the carbon dioxide reduction device of Example 1. FIG. 実施例2である二酸化炭素還元装置のCO生成量の比較グラフである。6 is a comparative graph of the amount of CO produced by the carbon dioxide reduction device of Example 2.

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。   Hereinafter, embodiments of the present invention will be described 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 the present 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. Yes. 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 under the liquid level of the solvent 40 along the container depth direction. Arranged. The lamp 30 is accommodated in a tubular protective member 32 such as a glass tube, and a sealed space into 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 performing electrolysis, an aqueous solution in which a soluble electrolyte is dissolved can be used, or an organic solution, an ionic solvent, or the like is also applicable. Here, an aqueous sodium sulfate solution is used as the solvent 40. Dissolution of carbon dioxide in the solvent 40 is performed 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 of solid carbon (hereinafter also referred to as a carbon substrate) formed in a single plate extending in the container depth direction. The carbon substrate 20 serving as a 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 weight concentration of boron 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 source (power feeding device) 36 is connected to the carbon material 20 and the metal plate 21, and 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 disposed 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 therethrough. The ion exchange membrane 60 partitions the reduction tank in which the carbon material 20 is disposed and the oxidation tank in which the metal plate 21 is disposed 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 on the substrate surface 20S of the carbon substrate 20 as a promoter. As shown in FIG. 2, silver particles are discrete and scattered on the substrate surface 20 </ b> S, 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 in which silver is supported on the substrate surface 20S, silver is deposited and sintered.

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。   Here, an electrodeposition method is used as a method for depositing silver on the substrate surface 20S. Specifically, by flowing a reduction current through the carbon substrate 20 in an aqueous silver nitrate solution, silver ions are electrolytically reduced and simultaneously 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 oxidation of silver. Here, heating is performed at a predetermined temperature for a predetermined time in a hydrogen atmosphere. The amount of silver carried 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 amount of reduction current, 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. While carbon dioxide is dissolved, power is supplied to the lamp 30 from a light source power source (not shown), 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 ultraviolet light emitted from the lamp 30, the carbon allotrope having the sp 3 crystal structure is excited and electrons are emitted. The relatively high light energy generated with this electron emission breaks the C═O bond of carbon dioxide (CO 2 ), and carbon monoxide (CO) is generated. The produced carbon monoxide 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 placed in the electrolyte solvent 40, a carbon dioxide reduction reaction for generating CO occurs. This CO-generated carbon dioxide reduction reaction substantially occurs only in a state in which a reduction reaction (photochemical reaction) based on a photocatalyst occurs.

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 that causes a redox reaction using the carbon material 20 and the platinum substrate 21 as a cathode (cathode) and an anode (anode), the carbon allotrope having the sp 3 crystal structure must be excited by ultraviolet light. For example, the CO-generated carbon dioxide reduction reaction 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 a CO-generated carbon dioxide reduction reaction is effectively generated, 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(S24 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) is applicable. Electrolyte dissociation and electrolysis produce sulfate ions (S 2 O 4 2− ), sodium ions (Na + ), hydrogen ions (H + ), etc., but only cations such as sodium ions and hydrogen ions 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, carbon dioxide dissolved in the solvent 40 and carbonate ions (such as CO 3 2− ) generated from the carbon dioxide cannot pass through the ion exchange membrane 60 together with the anions. As a result, the carbon dioxide dissolved in the solvent 40 is retained in the reduction tank by the bubble generator 17 installed in the reduction tank, and CO generation 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。   Further, 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, thereby further promoting the reduction of carbon dioxide. In particular, by depositing silver by an electrodeposition method using electrolytic reduction of silver ions, silver is deposited at the electron transfer site of the carbon substrate 20, and electrons can be efficiently supplied to the adsorbed carbon dioxide. . Further, since the entire surface of the substrate 20S is not covered with silver but is dispersed in a granular form (with a discrete distribution), 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 apparatus 10, the light source unit 35, the plate-like carbon material / carbon substrate 20 made of the carbon allotrope having the sp 3 crystal structure and having silver supported on the substrate surface 20S is provided. And placed in a solvent 40 in which carbon dioxide is dissolved. Furthermore, the platinum substrate 21 is disposed 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, ultraviolet light is irradiated from the lamp 30 toward the carbon material 20, and a voltage is applied to the carbon material 20 and the platinum substrate 21. By applying a voltage to the carbon material 20 that is a photocatalyst and carries silver as a cocatalyst together with ultraviolet light irradiation, CO is effectively generated.

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 for the carbon material. Alternatively, only a 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。   About precipitation of silver, you may use other than silver nitrate aqueous solution and may use the solution which silver ion melt | dissolved. Further, silver may be deposited by using an impregnation method or a light adsorption method instead of the electrodeposition method.

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。   It is possible to use a metal other than silver as a co-catalyst, and it may carry gold (Au), copper (Cu), platinum (Pt) having the same catalytic action, or a combination thereof including silver. It may be. That is, these metals have the same or equivalent ion valence when ionized, have d-orbits or f-orbitals as electron trajectories, 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, in Example 1, the effectiveness of the simultaneous process of light irradiation and voltage application to the photocatalyst will be described, and in Example 2, the effectiveness of silver support will be described.

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 apparatus of Example 1 is an apparatus corresponding to the present embodiment, but does not support silver on the carbon material surface. The carbon material is composed of a BDD substrate doped with 0.1% by weight of boron. The solvent is composed of an aqueous sodium sulfate solution. A Nafion membrane (registered trademark) is used as an ion exchange membrane that partitions 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。 For such a carbon dioxide reduction device, the amount of CO produced by carbon dioxide reduction was measured over time while changing the conditions. Specifically, the amount of CO produced was measured for the case where ultraviolet light irradiation was not performed, the case where only ultraviolet light irradiation was performed, and the case where both ultraviolet light irradiation and voltage application were performed. In the experiment, CO 2 was bubbled so that the solvent 40 had a concentration of 1.4 g / l, and a voltage of −1.8 V was applied to the BDD substrate and +1.8 V was applied to the platinum electrode. In addition, the amount of CO produced 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 amount of CO produced (μmol). As shown in FIG. 3, it is clear that CO generation does not occur only by voltage application. This indicates that even when electrolysis using a carbon material such as a BDD substrate as a cathode is performed, a reduction reaction of CO production 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 amount of CO produced significantly increased by both the ultraviolet light irradiation and the voltage application to the carbon material. It has been proved that applying a voltage to the carbon material having an excited sp 3 crystal structure promotes CO formation (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 of Example 2 is composed of a BDD substrate in which silver is supported on a carbon material as a cocatalyst and doped with 0.1% by weight of boron supporting silver by electrodeposition. . This carbon substrate was placed in a 25 mol / l sodium sulfate solution, and a platinum electrode was placed in a solution tank separated by an ion exchange membrane as a counter electrode. A voltage of −1.6 V was applied to the carbon substrate, and ultraviolet light with 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 that does not carry silver. However, the experimental conditions such as the applied voltage are the same as those in Example 2. As is apparent from FIG. 4, the amount of CO produced is significantly 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 supplier 60 Ion exchange membrane

Claims (10)

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-like carbon material containing a carbon allotrope having a sp 3 crystal structure, and at least one of gold (Au), silver (Ag), copper (Cu), and platinum (Pt) on the surface thereof A carbon material carrying a cocatalyst containing is disposed in the solvent as a photocatalyst,
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, thereby reducing carbon dioxide in the solvent, and carbon monoxide. The carbon dioxide reduction method characterized by producing | generating.
前記助触媒が、銀から成ることを特徴とする請求項1に記載の二酸化炭素還元方法。   The carbon dioxide reduction method according to claim 1, wherein the promoter comprises silver. 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ていることを特徴とする請求項1又は2に記載の二酸化炭素還元方法。   The carbon dioxide reduction method according to claim 1 or 2, wherein the promoter is dispersed in the form of particles on the surface of the carbon material. 前記電源の正極に接続したアノードを、前記溶媒中に配することを特徴とする請求項1乃至3のいずれかに記載の二酸化炭素還元方法。   The carbon dioxide reduction method according to any one of claims 1 to 3, wherein an anode connected to a positive electrode of the power source is disposed in the solvent. 前記炭素材と前記アノードとの間に、イオン交換膜を配置することを特徴とする請求項4に記載の二酸化炭素還元方法。   The carbon dioxide reduction method according to claim 4, wherein an ion exchange membrane is disposed between the carbon material and the anode. 前記炭素材に照射される紫外光の波長が、200nm〜260nmの範囲内であることを特徴とする請求項1乃至4のいずれかに記載の二酸化炭素還元方法。   5. The carbon dioxide reduction method according to claim 1, wherein a wavelength of ultraviolet light applied to the carbon material is in a range of 200 nm to 260 nm. 前記炭素材が、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ことを特徴とする請求項1乃至6のいずれかに記載の二酸化炭素還元方法。   The carbon dioxide reducing method according to any one of claims 1 to 6, wherein the carbon material has a boron-doped diamond structure having a boron weight concentration of 0.01% to 4%. 容器と、
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,
A solvent containing carbon dioxide dissolved in the container;
A plate-like carbon material disposed in the container and containing a carbon allotrope having a sp 3 crystal structure;
A light source that irradiates the carbon material with ultraviolet light that excites the carbon allotrope;
A power feeding device that connects the carbon material and the negative electrode and applies a voltage;
An anode disposed in the container and connected to a positive electrode of the power supply device;
Carbon dioxide, characterized in that a cocatalyst containing at least one of gold (Au), silver (Ag), copper (Cu), and platinum (Pt) is supported on the surface of the carbon material. Reduction device.
前記炭素材が、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ことを特徴とする請求項8に記載の二酸化炭素還元装置。   9. The carbon dioxide reducing apparatus according to claim 8, wherein the carbon material has a boron-doped diamond structure having a boron weight concentration of 0.01% to 4%. 二酸化炭素還元装置の溶媒中に光触媒として配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、
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 disposed as a photocatalyst in a solvent of a carbon dioxide reduction device,
A reduction current is passed through 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 carbon substrate on which the metal is deposited is a manufacturing method for sintering 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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