WO2011135782A1 - 二酸化炭素を還元する方法 - Google Patents
二酸化炭素を還元する方法 Download PDFInfo
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- WO2011135782A1 WO2011135782A1 PCT/JP2011/002069 JP2011002069W WO2011135782A1 WO 2011135782 A1 WO2011135782 A1 WO 2011135782A1 JP 2011002069 W JP2011002069 W JP 2011002069W WO 2011135782 A1 WO2011135782 A1 WO 2011135782A1
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- the present invention relates to a method for reducing carbon dioxide.
- a carbon dioxide (CO 2 ) reduction technique using a catalyst is expected as a technique for fixing CO 2 and producing useful substances.
- This reduction technology is one of the important means for solving the global warming problem caused by greenhouse gases that are expected to become apparent in the future.
- catalytic hydrogenation methods and electrochemical methods have been studied as CO 2 reduction techniques using catalysts.
- CO 2 is catalytically reacted with hydrogen (H 2 ) and reduced under high temperature and high pressure gas phase conditions.
- H 2 hydrogen
- Patent Document 1 and Patent Document 2 By catalytic hydrogenation, CO 2 can be converted into a highly useful substance such as methanol
- the reduction reaction proceeds even at room temperature and normal pressure.
- the electrolytic reduction method does not require large-scale equipment.
- the electrolytic reduction method is simpler than the catalytic hydrogenation method. From this, the electrolytic reduction method is considered as one of the effective CO 2 reduction methods.
- catalysts capable of reducing CO 2 using an electrolytic reduction method so far solid solid metals such as copper (Cu) and silver (Ag) and their alloy materials, and cobalt (Co), nickel ( Complex materials (molecular catalysts) such as Ni) and iron (Fe) have been developed (Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3).
- CO 2 is a very stable molecule. Therefore, the reduction treatment of CO 2 by the catalytic hydrogenation method requires a high temperature (heating temperature: 300 ° C.) and a high pressure (reaction pressure: 50 atm) to advance the reaction. Further, in the catalytic hydrogenation method, a combustible gas such as H 2 is used. For these reasons, the catalytic hydrogenation method requires large-scale equipment introduction. The catalytic hydrogenation method has a problem that a large amount of input energy is required for the reduction treatment and energy use efficiency is very low.
- the solid simple metal and alloy materials and the molecular materials used as catalysts in the electrolytic reduction method have a durability problem such that the deterioration due to a long-term catalytic reaction is severe.
- a catalyst that can reduce CO 2 by the electrolytic reduction method and has high practicality has not yet been found.
- an object of the present invention is to reduce CO 2 under an overvoltage condition equivalent to or smaller than that of a conventional catalyst, and to obtain highly useful substances (formic acid (HCOOH), methane (CH 4 ), ethylene (C 2 H 4). ) And ethane (C 2 H 6 ), etc.), and a method for reducing carbon dioxide using a highly durable catalyst.
- the present invention is a method for reducing carbon dioxide, comprising the following steps: Preparing an electrochemical cell (a), wherein: The electrochemical cell includes a working electrode, a counter electrode, and a tank, The tank stores electrolyte, The working electrode contains at least one nitride selected from the group consisting of titanium nitride, zirconium nitride, hafnium nitride, tantalum nitride, molybdenum nitride, and iron nitride, The electrolyte contains carbon dioxide; The working electrode is in contact with the electrolytic solution, The counter electrode is in contact with the electrolyte solution, and a negative voltage and a positive voltage are respectively applied to the working electrode and the counter electrode to reduce the carbon dioxide (b).
- an electrochemical cell in the method for reducing carbon dioxide of the present invention, is used.
- the electrochemical cell includes a working electrode that reduces carbon dioxide, the working electrode comprising a group consisting of titanium nitride, zirconium nitride, hafnium nitride, tantalum nitride, molybdenum nitride, and iron nitride.
- highly useful substances such as HCOOH, CH 4 , C 2 H 4 and C 2 H 6 can be produced under an overvoltage condition equivalent to or smaller than that of the conventional method. Furthermore, since the nitride has high durability, the working electrode can achieve high durability.
- Tantalum nitride (TaN) is when used, methane by gas chromatography (CH 4), shows the result of component analysis ethylene (C 2 H 4) and ethane (C 2 H 6).
- tantalum nitride When tantalum nitride (TaN) is used, it shows a component analysis result of carbon monoxide by gas chromatography (CO) and methane (CH 4). The figure which shows the component analysis result of formic acid (HCOOH) by a liquid chromatograph when tantalum nitride (TaN) is used.
- FIGS. 7A to 7C show reaction current-electrolytic potential measurement (CV measurement) when titanium nitride (TiN), molybdenum nitride (MoN + Mo 2 N) and iron nitride (Fe 2 N + Fe 4 N) are used. The figure which shows a result, respectively.
- the method for reducing carbon dioxide (CO 2 ) of the present invention is a method for electrochemically reducing CO 2 .
- an electrochemical cell is first prepared.
- the electrochemical cell includes an electrode (working electrode) used to reduce CO 2 .
- the working electrode is titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), tantalum nitride (TaN), molybdenum nitride (at least one selected from MoN and Mo 2 N) , And iron nitride (at least one selected from Fe 2 N and Fe 4 N).
- tantalum nitride is used for the working electrode.
- a slurry solution is prepared in which tantalum nitride particles (TaN particles) having an average particle diameter of about several ⁇ m obtained by nitriding are dispersed in an organic solvent. Then, an appropriate amount of the slurry solution is applied to conductive carbon paper (CP) woven with carbon fibers used as an electrode substrate. Thereby, a working electrode (catalyst) in which TaN particles are supported on CP is produced. CP is porous. Therefore, it is difficult to clearly define the amount of TaN particles supported. However, the amount of TaN particles supported is approximately several tens of ⁇ g / cm 2 to 1 mg / cm 2 .
- the electrode substrate is not limited to CP as long as it has conductivity.
- an inert metal substrate such as gold (Au), a glassy carbon substrate, and a conductive silicon substrate are generally used.
- the production method and shape of TaN particles are not limited.
- thin film TaN may be used. Even with an electrode structure in which TaN is deposited in a thin film on the surface of the conductive substrate by a method such as sputtering, the same catalytic activity as when particles are supported can be obtained. In such an electrode manufacturing method, impurities may be mixed in during the manufacturing process. However, catalytic activity appears depending on the type of compound used as the catalyst. Therefore, impurities mixed in during the preparation process do not affect the result of the catalytic activity of the compound.
- the configuration of the catalyst for CO 2 reduction containing TaN has been described as an example.
- tantalum nitride not only tantalum nitride, but also titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), molybdenum nitride (MoN and Mo 2 N), and iron nitride (Fe 2)
- TiN titanium nitride
- ZrN zirconium nitride
- HfN hafnium nitride
- MoN and Mo 2 N molybdenum nitride
- Fe 2 iron nitride
- the electrode substrate and the shape of the nitride supported on the substrate are various.
- an electrolytic reaction in an electrolytic solution or the like or an electrolytic reaction using a gas diffusion electrode is performed. Therefore, in order to stably carry or form the nitride on the substrate, it is necessary to adjust the carrying method and the film forming method suitable for each substance.
- a product obtained by CO 2 reduction using this working electrode includes a gas component (gas component) and a liquid component.
- a gas chromatograph is used for gas component analysis
- a liquid chromatograph is used for liquid component analysis.
- FIG. 1 shows CO adsorption energy values (E a ) on a single metal Ta surface and a nitride TaN surface estimated from a simulation (electronic state calculation) based on density functional theory.
- E a CO adsorption energy values
- single metal Ta and nitride TaN are compared.
- its E a value increases to ⁇ 5.86 eV. Therefore, when single metal Ta is used as the working electrode, CO is strongly adsorbed on the surface of single metal Ta, and it is predicted that the catalytic reaction hardly proceeds.
- Ta is nitrided as in the present invention, the E a value of CO decreases to about ⁇ 1.3 eV.
- an adsorption structure with relatively small energy is confirmed on the TaN surface even in CO 2 adsorption. Therefore, it is considered that the adsorption between the TaN surface and CO, and the adsorption between the TaN surface and CO 2 are not too strong, and the catalytic reaction is very likely to occur.
- the metal nitride (TaN, TiN, ZrN, HfN, MoN, Mo 2 N, Fe 2 N and Fe 4 N) used in the method for reducing CO 2 of the present invention, as described above, 2 can be adsorbed on the solid surface with small adsorption energy. This suggests that the nitride can reduce the CO 2 reduction overvoltage.
- the nitride used as a catalyst when reducing CO 2 enables a CO 2 reduction reaction with only external energy from a DC power source at room temperature.
- the method for reducing CO 2 of the present invention can be applied to a method using a solar cell as an external power source.
- This catalyst for reducing CO 2 can be combined with a photocatalyst and developed into a catalyst capable of using solar energy.
- the method of reducing the CO 2 using the nitride can be carried out by a method of blowing CO 2 gas into the electrolytic solution or a method of forming a three-phase interface using a gas diffusion electrode, and is very simple. . Therefore, it can be said that the method of reducing CO 2 using the nitride is a very promising technique as an energy-saving CO 2 countermeasure in homes and areas where so-called large-scale facilities cannot be introduced.
- the electrochemical cell of the present embodiment includes a working electrode 21, a counter electrode 23, and a tank 28, as shown in FIG.
- the tank 28 stores an electrolytic solution 27.
- the working electrode 21 and the counter electrode 23 are electrically connected to each other and are in contact with the electrolytic solution 27.
- the electrolytic solution 27 contains CO 2 .
- the tank 28 includes a solid electrolyte membrane (for example, a cation exchange membrane) 25.
- the solid electrolyte membrane 25 is disposed between the working electrode 21 and the counter electrode 23.
- the solid electrolyte membrane 25 separates the inside of the tank 28 into a region on the working electrode 21 side and a region on the counter electrode 23 side.
- the electrolytic chemical cell further includes a gas introduction pipe 26 that functions as a gas introduction port. One end of the gas introduction pipe 26 is disposed inside the electrolytic solution 27.
- a step of applying a negative voltage and a positive voltage to the working electrode 21 and the counter electrode 23 is performed. In this step, for example, CO 2 is supplied from the gas introduction pipe 26 to the electrolyte solution 27.
- the working electrode 21 is at least one selected from titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), tantalum nitride (TaN), and molybdenum nitride (MoN and Mo 2 N). ), And iron nitride (at least one selected from Fe 2 N and Fe 4 N).
- TiN titanium nitride
- ZrN zirconium nitride
- HfN hafnium nitride
- TaN tantalum nitride
- MoN and Mo 2 N molybdenum nitride
- Fe 2 N and Fe 4 N iron nitride
- the reference electrode 22 is a three-electrode cell provided with a reference electrode 22 because it is used for measurement in the examples.
- the reference electrode 22 since the measurement of the potential is not essential, the reference electrode 22 may not be provided.
- the material of the counter electrode 23 are metals such as platinum and nickel or metal oxides such as Cr 2 O 3 . When a material having a small overvoltage of the oxygen generation reaction generated at the counter electrode 23 is selected, carbon dioxide can be reduced with a lower applied voltage.
- the method for reducing CO 2 of the present invention can be carried out using the cell shown in FIG.
- this method first, an electrochemical cell as shown in FIG. 2 is prepared. Next, a negative voltage and a positive voltage are applied to the working electrode 21 and the counter electrode 23, respectively.
- the absolute value of the potential difference is preferably 2.0 V or more.
- An electrode used to reduce carbon dioxide at least one nitride selected from the group consisting of titanium nitride, zirconium nitride, hafnium nitride, tantalum nitride, molybdenum nitride, and iron nitride
- a catalyst for reducing carbon dioxide, comprising at least one nitride selected from the group consisting of titanium nitride, zirconium nitride, hafnium nitride, tantalum nitride, molybdenum nitride, and iron nitride catalyst.
- Example 1 Conductive carbon paper (CP) having a thickness of 0.3 mm was prepared as an electrode substrate. Tantalum nitride particles (TaN particles, purity: 99.9%) having an average particle diameter of 1 ⁇ m were supported on the CP with a distribution density of about 1 ⁇ 10 7 particles / cm 2 . In this way, the catalyst according to this example was produced. Using this catalyst, an electrochemical reduction reaction of CO 2 was performed.
- FIG. 2 shows a structural schematic diagram of the electrochemical cell used in this measurement. This electrochemical cell was a triode cell having a working electrode 21, a reference electrode 22 and a counter electrode 23. In this cell, the produced catalyst according to this example was used for the working electrode 21.
- a silver / silver chloride electrode As the reference electrode 22, a silver / silver chloride electrode (Ag / AgCl electrode) was used. A platinum electrode (Pt electrode) was used for the counter electrode 23.
- the triode cell was evaluated for CO 2 reduction by sweeping the potential with a potentiostat 24.
- a 0.1 M (0.1 mol / L) potassium hydrogen carbonate aqueous solution KHCO 3 aqueous solution
- the working electrode 21 and the counter electrode 23 are partitioned by a solid electrolyte membrane 25 in order to prevent mixing of gas components generated by catalytic action.
- the CO 2 gas was introduced into the electrolyte solution 27 by bubbling into the electrolyte solution 27 using a gas introduction pipe 26 disposed in the cell.
- the measurement was performed as follows. (1) First, nitrogen (N 2 ) gas was flowed into the electrolytic solution 27 at a flow rate of 200 ml / min for 30 minutes, and the bubbling state of N 2 gas was maintained. The potential was swept with CO 2 in the solution excluded, and a reaction current-electrolysis voltage curve (CV curve) was drawn. (2) Next, the piping was switched to CO 2 gas. CO 2 gas was also allowed to flow through the electrolyte solution 27 at a flow rate of 200 ml / min for 30 minutes, and the bubbling state of the CO 2 gas was maintained. The potential was swept while the electrolyte solution 27 was saturated with CO 2 , and a CV curve in the presence of CO 2 was drawn.
- N 2 nitrogen
- CV curve reaction current-electrolysis voltage curve
- FIG. 3 shows the result.
- a state in which the current value (vertical axis) is negative indicates that a CO 2 reduction reaction occurs.
- the reaction current changed from zero to minus when the potential E with respect to the silver / silver chloride electrode (Ag / AgCl electrode) was around ⁇ 0.9V.
- the product obtained by the CO 2 reduction reaction was analyzed.
- the gas component was analyzed using a flame ion detector (FID) type gas chromatograph.
- the liquid component was analyzed using a UV detection type liquid chromatograph.
- FIG. 4 shows the measurement results of methane (CH 4 ), ethylene (C 2 H 4 ), and ethane (C 2 H 6 ) by an FID gas chromatograph.
- this FID gas chromatograph a Porapak Q separation column was used. By controlling the valve with a preset time sequence, the FID gas chromatograph shows CH 4 around 1.5 minutes after the start of measurement, C 2 H 4 around 4.5 minutes, and around 6.5 minutes. Were programmed to detect C 2 H 6 respectively.
- voltage peak values were observed in the time domain corresponding to them. That is, it was confirmed that CH 4 , C 2 H 4 and C 2 H 6 were generated.
- FIG. 4 shows the measurement results of methane (CH 4 ), ethylene (C 2 H 4 ), and ethane (C 2 H 6 ) by an FID gas chromatograph.
- a Porapak Q separation column was used.
- the FID gas chromatograph shows CH 4 around 1.5 minutes after the start of measurement, C 2 H 4 around 4.5 minutes,
- FIG. 5 shows measurement results of carbon monoxide (CO) and the like by an FID gas chromatograph.
- FID gas chromatograph a Porapak N separation column was used.
- the valve is controlled according to a preset time sequence in the same manner as before, so that the FID gas chromatograph shows CO around 3.2 minutes after the start of measurement and CH 4 around 7.2 minutes. Programmed to be detected.
- a voltage peak value was observed in the time domain corresponding to each. That is, it was confirmed that CO and CH 4 were generated.
- FIG. 6 shows the measurement results of formic acid (HCOOH) by high performance liquid chromatography.
- HCOOH formic acid
- a TSK-GEL SCX (H + ) column was used.
- the liquid chromatograph was set so that a peak of HCOOH appeared around 11.5 minutes after the start of measurement.
- a voltage peak was obtained in this time region. That is, it was confirmed that HCOOH was also generated by electrolytic reduction of CO 2 using TaN.
- Example 2 Titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), molybdenum nitride (Mo 2 N and MoN), and iron nitride (Fe 2 N and Fe 4 N) were used as catalysts for reducing CO 2 .
- TiN titanium nitride
- ZrN zirconium nitride
- HfN hafnium nitride
- Mo 2 N and MoN molybdenum nitride
- Fe 2 N and Fe 4 N iron nitride
- FIG. 7A shows the reduction current of CO 2 when a catalyst having TiN particles is used.
- FIG. 7B shows the CO 2 reduction current when a catalyst having MoN particles + Mo 2 N particles is used.
- FIG. 7C shows the CO 2 reduction current when a catalyst having Fe 2 N particles + Fe 4 N particles is used.
- the CO 2 reduction current was confirmed from about ⁇ 0.8 V with respect to the Ag / AgCl electrode.
- the CO 2 reduction current was confirmed to be about ⁇ 1.03 V with respect to the Ag / AgCl electrode.
- the CO 2 reduction current was confirmed from about ⁇ 0.75 V based on the Ag / AgCl electrode.
- Example 1 The CO 2 reduction current was measured using an electrode consisting only of CP used as the electrode substrate in Example 1. The reduction current of CO 2 was measured using the same method as in Example 1. As a result, no reduction current of CO 2 was observed. That is, the electrode consisting only of CP was inactive to CO 2 reduction. The product of the electrolytic reaction was only hydrogen (H 2 ).
- Comparative Example 2 As metal nitride other than the metal nitride selected in the present invention, nitride particles of vanadium (V), chromium (Cr) and tungsten (W) were produced. These nitride particles were supported on the CP used as the electrode substrate in Example 1 and used as a catalyst. Using this catalyst, the reduction current of CO 2 was measured. As a result, the same characteristics as CP used as the electrode substrate were shown. That is, when the catalyst of Comparative Example 2 was used, only H 2 was produced, and products such as hydrocarbons and HCOOH were not obtained.
- the nitride of an element selected from Ti, Zr, Hf, Ta, Mo and Fe which is a highly durable compound, can electrolytically reduce CO 2 with an overvoltage smaller than that of a conventional catalyst.
- these nitrides are used as catalysts for reducing CO 2 , so that products such as CO, CH 4 , C 2 H 4 , C 2 H 6 and HCOOH can be obtained. According to these nitrides, energy-saving CO 2 electrolytic reduction using only a DC power source at room temperature is possible.
- the catalyst used in the method for reducing CO 2 of the present invention can also be applied to a configuration that is more environmentally friendly.
- the method for reducing CO 2 of the present invention can be applied to a method using a solar cell as an external power source.
- a catalyst for reducing CO 2 can be combined with a photocatalyst and developed into a catalyst capable of using solar energy.
- the present invention is a highly durable compound, Ti, Zr, Hf, Ta, nitrides of an element selected from Mo and Fe are the CO 2 under smaller overvoltage than conventional catalyst for reducing CO 2 It has been demonstrated that electrolytic reduction is performed. These nitrides can generate CH 4 , C 2 H 4 , C 2 H 6, HCOOH, and the like from CO 2 with less energy. That is, the method for reducing CO 2 of the present invention can provide these useful substances at low cost from CO 2 .
- CO 2 reduction treatment technology using these nitrides (a method for reducing CO 2 and an electrochemical cell used in the method) is also effective as a CO 2 reduction technology for global warming countermeasures. is there. In the future, this CO 2 reduction treatment technology can be expected as a method for reusing resources with less environmental impact by combining with photocatalyst technology and solar power generation technology.
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Abstract
Description
電気化学セルを用意する工程(a)、ここで、
前記電気化学セルは、作用極、対極、および槽を具備し、
前記槽は電解液を蓄えており、
前記作用極は、チタニウム窒化物、ジルコニウム窒化物、ハフニウム窒化物、タンタル窒化物、モリブデン窒化物、および鉄窒化物からなる群から選択される少なくとも1種の窒化物を含有し、
前記電解液は二酸化炭素を含有し、
前記作用極は前記電解液に接しており、
前記対極は前記電解液に接しており、および
前記作用極および前記対極に負の電圧および正の電圧をそれぞれ印加し、前記二酸化炭素を還元する工程(b)。
二酸化炭素を還元するために用いられる電極であって、チタニウム窒化物、ジルコニウム窒化物、ハフニウム窒化物、タンタル窒化物、モリブデン窒化物、および鉄窒化物からなる群から選択される少なくとも1種の窒化物を含有する、電極。
二酸化炭素を還元する触媒であって、チタニウム窒化物、ジルコニウム窒化物、ハフニウム窒化物、タンタル窒化物、モリブデン窒化物、および鉄窒化物からなる群から選択される少なくとも1種の窒化物を含有する、触媒。
0.3mmの厚さを有する導電性カーボンペーパー(CP)が、電極基板として準備された。CP上に、1μmの平均粒径を有する窒化タンタル粒子(TaN粒子、純度:99.9%)が、約1×107個/cm2の分布密度で担持された。このようにして、本実施例に係る触媒が作製された。この触媒を用いて、CO2の電気化学的な還元反応が行われた。図2は、今回の測定に用いられた電気化学セルの構造模式図を示す。この電気化学セルは、作用極21、参照極22および対極23を備えた三極セルであった。このセルでは、作製された本実施例に係る触媒が、作用極21に用いられた。参照極22には、銀/塩化銀電極(Ag/AgCl電極)が用いられた。対極23には、白金電極(Pt電極)が用いられた。この三極セルに対して、ポテンショスタット24で電位を掃引することにより、CO2の還元反応の評価が行われた。電解液27には、0.1M(0.1mol/L)の炭酸水素カリウム水溶液(KHCO3水溶液)が用いられた。また、作用極21と対極23との間は、触媒作用により生成するガス成分の混合を防ぐために、固体電解質膜25で仕切られていた。CO2ガスは、セル内に配置されたガス導入管26を用いて電解液27中にバブリングさせることによって、電解液27中に導入された。
(1)最初に、窒素(N2)ガスが200ml/minの流量で電解液27中に30分間流されて、N2ガスのバブリング状態が保持された。溶液中のCO2が排除された状態で電位が掃引されて、反応電流-電解電圧曲線(C-V曲線)が描かれた。
(2)次に、配管がCO2ガスに切り替えられた。CO2ガスが、同じく200ml/minの流量で電解液27中に30分間流されて、CO2ガスのバブリング状態が保持された。電解液27がCO2で飽和した状態で電位が掃引されて、CO2存在下でのC-Vの曲線が描かれた。
状態(1)(電解液27からCO2が追い出された状態)と状態(2)(電解液27がCO2で飽和した状態)との間で、C-V曲線の差分がとられた。この差分により、CO2の還元による反応電流(以下、還元電流)が評価された。図3は、その結果を示す。この図においては、電流値(縦軸)が負となる状態が、CO2の還元反応が起こっていることを示している。図3に示されるように、本実施例による実験の結果、銀/塩化銀電極(Ag/AgCl電極)に対する電位Eが-0.9V付近で、反応電流がゼロからマイナスに推移した。すなわち、TaN粒子を有する触媒では、銀/塩化銀電極(Ag/AgCl電極)を基準に、約-0.9Vの印加電圧下でCO2の還元電流が観測された。これは、標準水素電極において、約-0.7Vで還元が始まっていることを意味する。一方、本測定系を用いて、TaNの代わりにCu単体を有する触媒を用いて、CO2の還元実験が行われた。その結果、CO2の還元反応を得るためには、-1.1Vよりも大きな印加電圧が必要であった。この結果は、TaNがCO2還元時の過電圧の低減に有効であることを示す。
CO2を還元する触媒に、窒化チタニウム(TiN)、窒化ジルコニウム(ZrN)、窒化ハフニウム(HfN)、窒化モリブデン(Mo2NおよびMoN)および窒化鉄(Fe2NおよびFe4N)を用いた例についても、実施例1と同様の実験が行われた。その結果、窒化タンタル(TaN)について得られた結果と同様に、CO2の還元電流が観測され、かつCO、CH4、C2H4、C2H6およびHCOOHなどの生成が確認された。また特に、TiN粒子、MoN粒子とMo2N粒子との混合粒子(MoN粒子+Mo2N粒子)、および、Fe2N粒子とFe4N粒子との混合粒子(Fe2N粒子+Fe4N粒子)については、TaN粒子と同様に、Cuよりも低過電圧下でのCO2の還元電流が観測された。図7Aは、TiN粒子を有する触媒を用いた場合の、CO2の還元電流を示す。図7Bは、MoN粒子+Mo2N粒子を有する触媒を用いた場合の、CO2の還元電流を示す。図7Cは、Fe2N粒子+Fe4N粒子を有する触媒を用いた場合の、CO2の還元電流を示す。TiN粒子を有する触媒を用いた場合、CO2の還元電流は、Ag/AgCl電極を基準に約-0.8Vより確認された。MoN粒子+Mo2N粒子を有する触媒を用いた場合、CO2の還元電流は、Ag/AgCl電極を基準に約-1.03Vより確認された。Fe2N粒子+Fe4N粒子を有する触媒を用いた場合、CO2の還元電流は、Ag/AgCl電極を基準に約-0.75Vより確認された。
実施例1において電極基板として用いられたCPのみからなる電極を用いて、CO2の還元電流が測定された。CO2の還元電流は、実施例1と同様の方法を用いて測定された。その結果、CO2の還元電流は観測されなかった。すなわち、CPのみからなる電極は、CO2の還元に対して不活性であった。電解反応による生成物は、水素(H2)のみであった。
本発明において選択された金属窒化物以外の金属窒化物として、バナジウム(V)、クロム(Cr)およびタングステン(W)の窒化物粒子が作製された。これらの窒化物粒子が、実施例1で電極基板として用いられたCPに担持されて、触媒として用いられた。この触媒を用いて、CO2の還元電流が測定された。その結果、電極基板として用いたCPと同様の特性が示された。すなわち、比較例2の触媒を用いた場合、H2のみが生成され、炭化水素およびHCOOHなどの生成物が得られなかった。
Claims (4)
- 二酸化炭素を還元する方法であって、以下の工程を具備する:
電気化学セルを用意する工程(a)、ここで、
前記電気化学セルは、作用極、対極、および槽を具備し、
前記槽は電解液を蓄えており、
前記作用極は、チタニウム窒化物、ジルコニウム窒化物、ハフニウム窒化物、タンタル窒化物、モリブデン窒化物、および鉄窒化物からなる群から選択される少なくとも1種の窒化物を含有し、
前記電解液は二酸化炭素を含有し、
前記作用極は前記電解液に接しており、
前記対極は前記電解液に接しており、および
前記作用極および前記対極に負の電圧および正の電圧をそれぞれ印加し、前記二酸化炭素を還元する工程(b)。 - 請求項1の方法であって、
工程(b)においてメタン、エチレン、エタン、および蟻酸からなる群から選択される少なくとも1種の化合物が生成する。 - 請求項1の方法であって、
前記槽は固体電解質膜を具備し、
前記固体電解質は、前記作用極および前記対極との間に挟まれている。 - 請求項1の方法であって、
前記電気化学セルは管を具備し、
前記管の一端は、前記電解液の内部に配置されており、
前記工程(b)において、前記管から前記二酸化炭素が前記電解液に供給される。
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