JPH04136751A - Electrode for measuring concentration of carbon dioxide - Google Patents

Abstract

PURPOSE:To make the title electrode small in size by a method wherein an organic film having a terpyridene derivative ligand - transition metal complex fixed thereto and having a reducing catalyst power for a carbon dioxide gas is applied on a conductive base and the electrode is constructed as an electrode of an entire solid film type. CONSTITUTION:An electrode for measuring the concentration of carbon dioxide is provided with a conductive base and an organic film having a terpyridence derivative ligand - transition metal complex fixed thereto, having a catalyst power for a carbon dioxide gas and covering the aforesaid conductive base, and measures the concentration of the carbon dioxide gas from a reduction current value thereof by an amperometric method. In other words, a transition metal of cobalt or ruthenium is used as a catalyst for reducing the carbon dioxide gas, according to the present invention. By combining a bulky styryl group in the vicinity of this transition metal, it is made easy for the carbon dioxide gas permeate through the film and the contact of the metal complex of cobalt or ruthenium with the carbon dioxide gas is facilitated. As the result, a reducing reaction is promoted and the precision in measurement is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electrode for measuring the concentration of carbon dioxide gas (CO□), and particularly relates to a carbon dioxide concentration measuring electrode for measuring the concentration of carbon dioxide gas (CO□). Reduction reaction using a catalyst,
The present invention relates to an electrode for measuring carbon dioxide concentration, which measures the concentration of carbon dioxide gas by measuring the reduction current value using an amperometric method (current method).

[Prior art and problems to be solved by the invention] As an electrochemical reduction method for carbon dioxide gas, Fischer et al. used zinc amalgam as a cathode and potassium sulfate (
It was the first time that the formation of formic acid ()IcOO)I) was observed by electrolytically reducing carbon dioxide gas dissolved under pressure in an aqueous solution (Ber, dt, Chem, Ges).
, 47256 (1914>). Recently, Kaname Ito et al. have used zinc, lead, and other materials, which have a relatively high hydrogen overvoltage, instead of mercury.
Using solid metals such as tin, indium, and cadmium, we investigated the formation of formic acid as the main product in an aqueous inorganic salt solution.
Confirmed by V absorption spectrum (Bull.

Nagoya In5t, of Tech 27209
(1975)). In addition, Hori et al.
We conducted experiments using copper (C HCO+) and various metal electrodes.
u), methane (CH4), gold (^U) or silver (
We found that -carbon oxide (CD) was selectively produced in 8g) (Y, Hori, K.

Kikuchi, S., 5uzuki J., Am.
, Chem, Soc, 1095022 (1987
)). Furthermore, in the rear trunk, ethylene (C21'14)
It was also revealed that similar products can be obtained by electrolytic reduction of -carbon oxide, suggesting that the reduction reaction of carbon dioxide occurs via carbon monoxide.

In addition, in the American Chemical Society (AC3) Symposium Series 363 “Catalytic Carbon Reduction Method”, bipyridine rhenium carbonyl chloride [Re(bpY) (CD)
sc1, rhodium bipyridine ([Rh(bpyL]
-) A carbon dioxide reduction reaction using a catalyst has been reported.

Furthermore, J. Evans et al. bis-1,3-propanediamine sulfate copper(n) (Cu(II) bi
s-1゜3-propanediamine 5ulf
A new electrochemical carbon dioxide sensor (
J, Blectronal Chem.

262 (1989) 119-129).

Also, vinylbiviridine rhenium chloride ([ReC0, (V-
bllV)CI] -) Film (J, Blectr
onal Chem, InterfacialEl
electrochem, 09(1) 101-107
(1986)) and bis(vinylterpyridine)] ([Co(V-tpy)z]") electropolymerized membranes (Inerg, Chem, 28 (6) 1080
-1084 (1989)) was reported on the reduction reaction of carbon dioxide.

As mentioned above, various reports have been made to date, but these reports focus on the electrochemical behavior of metal complex compounds that undergo a reduction reaction with carbon dioxide and their electrolytically polymerized membranes. No electrode for measuring carbon dioxide concentration has been reported that can control and measure dissolved carbon dioxide gas with high accuracy.

The present invention has been made in view of these problems, and an object of the present invention is to provide a carbon dioxide concentration measuring electrode that is small in size and can measure the concentration of carbon dioxide gas with high accuracy.

[Means to solve the problem]

The electrode for measuring carbon dioxide concentration according to the present invention includes a conductive substrate, a terpyridine derivative ligand-transition metal complex fixed thereon, and a carbon dioxide gas catalytic ability, and an organic film covering the conductive substrate. The concentration of carbon dioxide gas is measured using the IJ hook method based on the reduction current value of carbon dioxide gas.

As the conductive substrate, noble metals such as platinum and gold, and BPG are used.
A conductive carbon material such as (basal plain pyrolytic graphite) is used.

Specifically, the organic film is 4'-styryl-2,2';
A polymer made of a transition metal complex of 6',2'-terpyridine is used, and any transition metal that has a catalytic ability for carbon dioxide gas may be used (such as cobalt (CO), etc.).
), Ruthenium (Ru), Iron (Fe), ? Ngan (M
o), nickel (Ni), etc. are used.

That is, in the present invention, a transition metal such as cobalt or ruthenium is used as a catalyst for reducing carbon dioxide gas, and by bonding a bulky styryl group near this transition metal, carbon dioxide gas is reduced in the membrane. It becomes easier to permeate and the metal complex of conoclusite or ruthenium can easily come into contact with carbon dioxide gas. As a result, the reduction reaction is promoted and measurement accuracy is improved.

Although this organic film may be formed by coating directly on the conductive substrate, it is preferable to form the organic film by electrolytic polymerization.

As the electrolyte salt used in electrolytic polymerization, it is preferable to use n-tetrabutylammonium salt (n-Bu4NX) or tetraethylammonium salt (εt4NY).

Note that X and Y are each perchlorate ion (ClO2-
), tetrafluoroborate ion (BF4-),
Trifluoromethylsulfite ion (CF3SO3
-), bromine ion (Br-), and toluenesulfonic acid ion (CH3CsHaSOs -).

In the electrolytic polymerization of 4'-styryl-2,2';6',2'-terpyridine using a cobalt metal complex, the influence of the electrolyte salt, especially the anion group, is large. For example, n-tetrabutylammonium tetrafluoroborate-acetonitrile (nBuJBF4-CHsCN) as a salt.
When this system is used, the complex is coated as a polymer film on a conductive substrate such as a BPG substrate in about 40 minutes. On the other hand, the electrolyte salt is n-tetrabutylammonium perchlorate-acetonitrile (n-Bu4NC10, -CH5
In the case of the CN) system, it is difficult to form a polymer film on a BPG substrate, and the time required for electrolytic polymerization is 4 hours or more, and moreover, only a small amount of a polymer film is formed on the BPG substrate.

In addition, organic solvents used in electrolytic polymerization include acetonitrile (CH, CN), tetrahydrofuran ((:
, H80), dimethylfuran (C6H80),
Benzonitrile (C6H5CN), Nitromethane (CH
, NO□), dimethyl sulfoxide ((cHiLs
o)), dimethylformamide (HCON(CH,
) 2) or dimethylamine ((CH8) 2N
H) can be used. This organic solvent also affects the electrolytic polymerization reaction. Specifically, BP is used as the conductive substrate.
When a G substrate is used and a tetrabutylammonium salt is used as the electrolyte salt, comparing acetonitrile solution and dimethylformamide solution as organic solvents, the cobalt redox peak is reversible in the former system, whereas the cobalt redox peak is reversible. In the latter case, the peak becomes broad. This is because the complex effect of the dimethylformamide solvent is large, and it is thought that the dimethylformamide solvent behaves similar to a type of hydration reaction.

In addition to the electrolytic polymerization method, organic films can be formed by preparing a polymer containing a transition metal in advance, dissolving it in an organic solvent, and coating it on a conductive substrate using a coating method, dielectric method, etc. You may also do so.

〔Example〕

Examples of the present invention will be specifically described below.

(Example 1) (1) 4'-styryl-2,2'; As the reagent for synthesizing 6',2' terpyridine, commercially available special grades were used as they were unless otherwise specified. Activated alumina for column separation is activated alumina 5QA.
ctive (manufactured by Merck & Co.) was used. Moreover, the water used as a solvent was distilled twice.

[1] to [7] in FIG. 3 indicate the following reaction steps, respectively.

[1] Synthesis of (2-pyridoacyl)-pyridinium iodide 2-acetylpyridine 9.26 rrd! (8,25
X 10-”mol/l) Pyridine 30mf (3,
71Xl0-'mol/f), iodine 22g (1
, 73
The mixture was heated to 95° C. over a period of time. At this time,
Stirring became impossible due to the precipitation of a large amount of crystals, but the reaction vessel was kept at 95 to 100 °C for an additional 30 minutes.
After the reaction was completed, the reaction mixture was washed with benzene to remove excess pyridine and iodine. The obtained crude product was recrystallized four times from a mixed solvent of ethanol and water (20:21 v/v) to obtain metallic luster crystals (yield 78%).

[2] Synthesis of 2 (1-oxo-5-(4-methylphenyl)prop-2en-1yl)-pyridine 5.61 ml of 2-acetylpyridine! (5XIO ”mol/
1> and p−) 5.90 ml of toluenaldehyde (5X
IO-2 mol/j) was added thereto, and 10 mf of a 3% by weight sodium hydroxide-methanol solution was added dropwise while stirring. After standing in this state for one night, stirring was stopped and the solvent was distilled off by heating, and the mixture was left standing at 5°C for half a day. The crystals precipitated at this time were suction filtered, washed with cold methanol, and subjected to the next reaction without any particular purification (yield: 59%).

[3] Synthesis of 2.6-bis(2-pyridyl)-4-(4-methylphenyl)pyridine 9.28 g of the crystalline compound obtained in [1] in 100 methanol (2,85X 10-2 mol/ R)
and [6.35 g of the crystalline compound obtained in 21 (2,8
5X 10-" mol/R) and 22 g (2,85 After suction filtration, such crystals were recrystallized from an acetone solution to obtain white crystals.The product was identified using 200 MHz 'HNMR (manufactured by Hitachi Seisakusho). The results are shown in Figure 4. In the figure, δ represents the amount of proton chemical shift (PPm) in the 200M)Iz'H NMR spectrum.The white crystals obtained from this result are 2.6-bis( It was confirmed that it was 2-pyridyl)-4(4-methylphenyl)pyridine.

[4] Synthesis of 2.6-bis(2-pyridyl)-4-(4-bromomethylphenyl)pyridine In 30 mj' of carbon tetrachloride, compound 3 obtained by
g (9.

28
), and further benzoyl peroxide (BPO)
After adding 60 mg (2,48Xl0-'mol/1), the mixture was refluxed for about 3 hours. After the reaction was completed, the solvent was completely distilled off, and the reaction mixture was washed with water to remove the succinimide. The obtained crude product was recrystallized from chloroform/methanol to obtain light green crystals (yield 86%).
).

[5] Synthesis of 2.6-bis(2-pyridyl)-4-(4-methylphenyl)pyridine-triphenylbromophosphonium Add 2 g of the crystals obtained in [4] to 100% of dehydrated acetone.
(4.

97 X 10-'mol/j! ) and 1.3 g of triphenylphosphine (4,96Xl0-'m
After adding ol/j, the mixture was refluxed for about 4 hours. At this time, a white precipitate was observed, but the mixture was cooled for half a day to separate out the precipitate. The resulting precipitate was filtered, and the filtrate was concentrated and cooled, and the resulting precipitate was added thereto. The obtained white solid was confirmed to be the intended triphenylphosphonium salt from an infrared spectrum.

[6] 4'-Stiryl 2.2';6', 2
"Synthesis of terpyridine [5] Without purification, the white solid obtained was immediately suspended in a 20% formalin solution, and 5% hydroxylated with stirring at room temperature). After the dropwise addition was completed, stirring was continued for 3 hours at room temperature.

The resulting precipitate was filtered, thoroughly washed with water, and then dried under reduced pressure at room temperature. Thereafter, it was isolated using an alumina column (diameter 1.5 cm x length 20 cm) using chloroform solvent. Furthermore, white crystals were obtained by recrystallizing from acetone (yield 69%). The obtained product was identified using 200Mflz'HNMR (manufactured by Hitachi Seisakusho). The results are shown in FIG. The white crystals obtained from this result were 4'-styryl-2,2';6',2''
It was confirmed that it was terpyridine.

(2) Formation of cobalt complex [7] Bis(4'-styryl-2,2';6'
, 2” Synthesis of cobalt-hexafluorophosphate monohydrate [6] 369 mg (1,2 mM
/ 1) and cobalt chloride hexahydrate (140 mg (0
, 59mM/1) in water (30d) at room temperature for 4 hours, ammonium hexafluorophosphate (200μ (1,25mM/1)) was added to precipitate the complex as a salt.The salt was dissolved in cold ethanol. The crystals were washed with water and dried under reduced pressure at room temperature to obtain crystals (dark brown).

(3) Electrolytic polymerization of cobalt complex Next, as shown in FIG. 1, a platinum substrate (electrode area 7°85×10−
'crl) 11, the periphery thereof was insulated with a tear c+inch nive 13, and the gap was covered and insulated with an epoxy resin layer 14, thereby producing a platinum electrode 15. This is used as the working electrode as shown in Figure 2, and the chain line (Ag) is used as the reference electrode.
16. Using a platinum mesh (Pt) 17 as a counter electrode, electrolytic polymerization was performed in the following electrolyte solution 18 to form a cobalt complex film 19 on the platinum electrode 15.

The reaction time was 48 minutes.

1.0mM 4'-styryl-2,2';6',
2'-terpyridine-cobalt complex (pH=6.2) 0
, LM n-tetrabutylammonium tetrafluoroborate (n-Bu4NBF 4 ) Solvent Acetonitrile solution (nitrogen atmosphere) The cyclic portamogram of this complex is shown in FIG. 6(a). Acid amount redox potential is 0. IV -0°91V, -1,72V
(vs. Ag) +: Current t'L, each heek haso Co
(III)/(II) vs. Co(II)/, (1
) vs. C.

A reversible redox response corresponding to the (I)/(0) pair is shown. However, the sweep was repeatedly performed in the range of 0.6 V to -2, OV (person-to-person g). As a result, it was found that an organic thin film was formed on the surface of the platinum electrode 15 and a cobalt complex was formed in the polymer.

Experimental Example 1 Next, regarding the oxidative polymerization reaction of the platinum/cobalt complex membrane electrode prepared in Example 1, Co(III)/(I
The cyclic portammograms of the Co(II)/(I) pair and the Co(II)/(I) pair are shown in FIG. 6(b). Here,
The solid line A shows the case where the number of sweeps is 20 (seconds/cycle), and the broken line B shows the case where the number of sweeps is 32 (seconds/cycle). In this experimental result, as the number of sweeps increases, the peaks change from Co(II)/(I) vs. > Co(II
I) / (■) pair order. This suggests that the reaction of the Co(II)/(I) pair in the polymer film is likely to occur.

Experimental Example 2 Using the platinum/cobalt complex membrane electrode prepared in Example 1, a cyclic portamogram was observed under the following conditions.

The sweep speed was 5.0+nV/S.

Buffer solution 0.1M n-tetrabutylammonium tetrafluoroborate (n-Bu4NBF4) Solvent Acetonitrile solution (nitrogen atmosphere) Figure 7(a) shows the results, and the oxidation potential of the cobalt complex is -0.65V. (
vs. AgC+).

Experimental Example 3.4 Carbon dioxide gas was introduced into the nitrogen system of Experimental Example 2, and a cyclic portamogram was observed. The results are shown in Figure 7 (
b) Expressed in As a result, the reduction peak of carbon dioxide gas was at -0.67V, Experimental Example 2 (Nitrogen atmosphere)
It was confirmed that the redox current value of carbon dioxide gas increased compared to the case of . However, in this experiment, the sweep rate was 200 mV/S. Current value increase is approximately 14μA
and small (0.67 V vs. Ag). Next, Figure 7 (C
) represents the result when oxygen gas is introduced into this system. In this result, -1,12V (vs. Ag)
An oxygen reduction peak appears. That is, a peak was observed in the negative direction by 0°45V from the peak when carbon dioxide gas was introduced. From this result, it was found that the reduction current values of carbon dioxide gas and oxygen gas could be separated.

(Example 2) Electrolytic polymerization was carried out under the same conditions as in Example 1, except that a conductive carbon electrode (Nippon Carbon EG511, electrode surface area: 0.049c++) was used in place of the platinum electrode 15 of Example 1.

The cyclic portamogram in this case is shown in Figure 8(a).
Shown below. The sweep speed was 100 mV/S, +o, g
v ~ -2,0V (vs. Ag) (7) Range II sweep was repeated 11 times. Co(III)/(II) vs. C
The peaks of reversible redox reactions corresponding to the o (II)/(1) pair and the Co (I)/(0) pair are +〇 and 0, respectively.
8V, -0,92V, -1,72V (vs Ag)
appeared on. From this result, it was confirmed that a 4'-styryl-2,2';6'+2'-terpyridine-cobalt complex film was formed on the surface of the conductive carbon electrode. Furthermore, the current response peak of the cobalt redox reaction in the cyclic portamogram of the electrode of Example 1 in which a platinum substrate was coated with a cobalt complex film was larger in this example. The reason for this is that when the substrate material is platinum, it is more easily activated than carbon material, so the redox response of the complex (Co) in the film appears small.
This is thought to be due to the fact that in carbon materials that are difficult to activate, the redox response of the complex in the film appears significantly, and as a result, a clear peak appears as shown in Figure 8(a).

Experimental Example 5 Using the BPG/cobalt complex membrane coated electrode of Example 2,
Figure 8(b) shows the cyclic portammogram when a potential of +1.8V (vs. Ag) is applied in the oxidation direction.
Expressed in As is clear from this figure, as the sweep is repeated, the current peak of the Co(n)/(I) pair becomes C
o(II[)/(II) pair. On the other hand, from this experiment, a very large redox peak is observed between +1.6v and 1.8v. This peak is
This is thought to be caused by activation of the quinone-hydroquinone type structure of the conductive carbon substrate. This result clearly shows that the Co(II)/(1) pairing reaction site in the film is easily activated.

Experimental Example 6 Example 20 A cyclic portamogram was observed in the following buffer solution using a BPG/cobalt complex membrane coated electrode. The results are shown in Figure 9(a). The sweep speed was 5.0+nV/S.

Electrolyte solution 0, IM n-tetrabutylammonium tetrafluoroborate (n-Bu, NBF4) Solvent Acetonitrile solution (nitrogen atmosphere) From this experiment, the oxidation potential of the cobalt complex was observed to be 10.5V (vs g) .

Experimental Example 7.8 Carbon dioxide gas was introduced into the system of Experimental Example 6, and a cyclic portamogram was observed in the same manner as in Experimental Example 6. The results are shown in Figure 9(b). This allows Co(II
) /(1) Redox current peak is -0°54v
(Person g), and it was observed that the current value increased by -1.3 μA due to the introduction of carbon dioxide gas compared to the system in a nitrogen atmosphere. Furthermore, a cyclic portammogram when oxygen gas is introduced is shown in Figure 9). In this case, an oxygen reduction current peak was observed near -0.8 V (vs. Ag). That is, when oxygen gas is introduced, the voltage is shifted to the negative side by 0.26 V compared to when carbon dioxide gas is introduced.

Therefore, under these experimental conditions, there was only a slight separation in the reduction current values between oxygen gas and carbon dioxide gas.

(Example 3) As the electrolytic polymerization conditions of Example 2, n-tetrabutylammonium tetrafluoroborate (n-Bu=NBF<)
Instead of n-tetrabutylammonium perchlorate (n
-Bu4NCIO4) is shown in Figure 10(a). Co(III)/(II) vs. C in this figure
The reversible redox reaction peaks corresponding to o(ff)/(I) pair and Co(I)/(0) pair are respectively +
0°185V, -0,69V, -1,48 (vs. Ag) L: Appears. However, -2゜OV ~ +0.8
V ltAg) (D range T:, sweep speed &100+++
The V/S sweep was repeated.

Experimental Example 9 Under the conditions of Example 3, +2, [lV (vs. Ag)
Figure 10(b) shows the cyclic portamograms of the [:o(III)/(II) pair and the Co(II)/(I) pair when a potential is applied in the oxidation direction up to .

However, the sweep was repeated at a sweep rate of 50 mV/S in the range of -1.0 V to +2°0 V (vs. Ag). C
o (I[I)/ (II) vs. Co (II)/ (
I) The current peaks corresponding to the pairs are +〇, 3 V, -, respectively.
It appears at 0°8V (interpersonal g), and Co (n)/
The current peak of the (I) couple is significantly increased than that of the Co(I)/(n) couple. On the other hand, +1.6V~
2. A very large redox wave was observed in the OV range. It is believed that this peak appears for the reason described in Experimental Example 5.

Experimental Example 10 A cyclic portamogram in the following buffer solution was observed using a BPG/cobalt complex membrane coated electrode coated by the electrolytic polymerization method of Example 3. The results are shown in FIG. However, the sweep speed was 5.0 mV/S.

Electrolyte solution 0, IN n-tetrabutylammonium perchloric acid (
n-BLI4NC104) Solvent Acetonitrile solution (nitrogen atmosphere) As a result, C
o The redox potential of the (I[I)/(II) pair is 10.
43 (vs. Ag), and then Co (II)/ (
I) The oxidation potential of the pair was observed to be -0.53 V (vs. Ag). As a result, it was confirmed by comparison with Figure 8(a) that the electropolymerization reaction peak was almost the same as that of the redox potential method, or slightly shifted to the oxidation side, and the magnitude of the current value at that time was also almost the same. It was found that a cobalt complex-containing polymer film was stably coated on top.

Experimental Example 11 A cyclic portamogram obtained when a dimethylfuran (DMF) solution was used instead of the acetonitrile solution in the buffer solution of Experimental Example 9 is shown in FIG. 12(a). From this experimental result, Co(II)/(I) pair,
Redox reaction peaks corresponding to the Co(I)/(0) pair appear at −0.5 V and −1.36 V (vs. g), respectively. However, the current peak at this time is slight.

Experimental Example 12 Next, FIG. 12(b) shows a cyclic portammogram obtained when the nitrogen-saturated system shown in FIG. 12(a) is changed to a carbon dioxide-saturated system. As a result, a current change due to the carbon dioxide reduction reaction appears at -1.4 V (vs. Ag). This change is significant, and there is a possibility that the DMF solvent (particularly proton supply) effect is also occurring.

〔Effect of the invention〕

As explained above, according to the electrode for measuring carbon dioxide concentration of the present invention, a terpyridine derivative ligand-transition metal complex is immobilized on a conductive substrate, and an organic film having a catalytic ability to reduce carbon dioxide gas is formed. Since the entire surface is coated with a membrane type electrode structure, it is possible to significantly reduce the size.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing the configuration of an electrode for measuring carbon dioxide concentration according to Example 1 of the present invention, and FIG. 2 shows a schematic configuration of an electrolytic polymerization apparatus used for forming an organic film of the electrode of Example 1. A vertical cross-sectional view, Figure 3 is a diagram showing the reaction process of forming an organic film, and Figure 4 is a diagram showing the reaction process of forming an organic film.
5 and 5 respectively show the identification results of the product in the step shown in FIG. 3, and FIGS. 6 and 7 show cyclic portamograms according to Example 1 of the present invention. Figure 6(a) is a diagram showing the results when electrolytically polymerizing an organic film, Figure 7(b) is a diagram showing the results in Experimental Example 1, Figure 7(a) is a diagram showing the results in Experimental Example 2, The same figure (b
) is a diagram showing the results in Experimental Example 3, the same figure (C) is a diagram showing the results in Experimental Example 4, and FIGS. , FIG. 8(a) is a diagram showing the results when electrolytically polymerizing an organic film, FIG. 8(b) is a diagram showing the results in Experimental Example 5, and FIG. 9(a) is a diagram showing the results in Experimental Example 6. The figure (b) is a figure showing the results of experiment example 7, and the figure (c) is a figure showing the results of experiment example 7.
Figures 10 to 1 show the results of Experimental Example 8.
Figure 2 shows cyclic portamograms according to Example 3 of the present invention, Figure 10 (a) shows the results of electrolytic polymerization of an organic membrane, and Figure 10 (b) shows the results of the experiment. Figure 11 shows the results in Experimental Example 10, Figure 12(a) shows the results in Experimental Example 11, and Figure 12(b) shows the results in Experimental Example 12. It is a diagram. 11...Platinum base 12...Lead wire 13...Teflon tube 14...Epoxy resin layer Applicant Terumo Corporation Company agent Patent attorney Yoichi Fujishima

Claims (1)

[Scope of Claims] 1. A conductive substrate, and an organic film having a terpyridine derivative ligand-transition metal complex fixed thereon and having a carbon dioxide gas reduction catalytic ability and covering the conductive substrate. An electrode for measuring carbon dioxide concentration, characterized by: 2. The electrode for measuring carbon dioxide concentration according to claim 1, wherein the surface of a conductive substrate is coated with the organic film by electrolytic polymerization. 3. The electrode for measuring carbon dioxide concentration according to claim 1, which is obtained by preparing a polymer having a transition metal in advance, dissolving the polymer in an organic solvent, and coating the conductive substrate thereon.