Diamond electrode

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a diamond electrode which is used in a chemical industry process, electrolysis, a battery, a photovoltaic power generation, a chemical sensor, etc., has a small overvoltage, has a long life, and can regenerate an electrode and measure the temperature of an electrode portion.

【0002】

[Conventional technology]

Diamond has excellent heat resistance and is characterized by a large energy gap of 5.5 eV. In addition, diamond has excellent electrical characteristics such as a large breakdown voltage and a high saturation drift rate and a low dielectric constant. Furthermore, diamond is stable to chemical reagents, has high thermal conductivity, low specific heat, excellent heat resistance, and has better physical properties than other substances such as less damage due to irradiation. ..

【0003】

Undoped diamond is an electrically insulator, but it has the property of lowering the electrical resistance of the diamond film by adding a small amount of impurities to the diamond synthesis raw material to synthesize the diamond film in a vapor phase. For example, high-temperature and high-pressure synthesis When boron is added as an impurity by the method or the vapor phase synthesis method, a P-type semiconductor diamond having excellent conductivity can be obtained. In such a semiconductor field, research on high temperature devices (temperature sensors, diodes, transistors, etc.) focusing on the heat resistance of diamond has been made, but diamond having excellent electrical and physical characteristics as described above has been studied. Studies utilizing the combined properties of the above are rare, and some of them have reported techniques for applying semiconductor diamond films to electrodes ((1) K. Patel et al, Proceedings of Joint Research Presentations by the Japan Solar Energy Society and the Japan Wind Energy Association in 1991 (September 20, 1991) pp.105-108; (2) K. Patel et al, J. Photochem. Photobiol. A: Chem., Vol.65, pp.419-429 (1992); (3) R.Tenne et al, J.Electroanal.chem.Vol.347, pp.409-415 (1993); (4) S .Yang et al, Advances in New Diamond Science and Technology, edited by Y. Saito et al (MYU, Tokyo 1994), pp.741-744). However, in these conventional techniques, a diamond film that has been synthesized and has not been subjected to any subsequent treatment is used for the electrode.

【0004】

Diamond films are used for microwave chemical vapor deposition (microwave CVD) (for example, Tokusho 59-27754, Tokusho 61-3320), high-frequency plasma CVD method, thermal filament CVD method, DC plasma CVD method, plasma jet. The vapor phase is synthesized by a method, a combustion method, a thermal CVD method, or the like. A diamond film gas-phase-synthesized on a non-diamond substrate such as silicon by these methods is generally a polycrystal in which diamond particles are irregularly aggregated, and grain boundaries are present at a high density. However, by special substrate surface treatment, it is possible to synthesize a diamond film in which crystal particles are aligned in substantially a certain direction, such as a highly oriented film or a heteroepitaxial film. Furthermore, in any film, the surface of the diamond film can be composed of only specific crystal planes, for example, (111) crystal planes or (100) crystal planes.

【0005】

For example, by cutting a bulk diamond along a specific crystal plane, polishing it, and then forming a diamond film on the surface of the bulk diamond, a diamond film having the specific crystal plane can be obtained, and thus, such A diamond film having an arbitrary crystal plane can be obtained.

【0006】

[Problems to be Solved by the Invention]

However, on the surface of such a diamond film, a film having a high hydrogen content and whose structure has not been confirmed remains. Therefore, diamond does not actually exist on the surface of the conventional diamond electrode. As a result, there is a problem that the characteristics as an electrode are inferior to the characteristics of the original diamond.

【0007】

Further, since the temperature of the electrode itself or the electrolyte solution in contact with the electrode is not measured and controlled, there is a problem that it is not possible to quickly respond to an abnormal situation such as overheating of the electrode.

【0008】

Further, in the prior art, a diamond film is used for the electrode, but there is also a problem that the manufacturing cost of the diamond film is high at present.

【0009】

The present invention has been made in view of the above problems, and provides a diamond electrode having a small overvoltage, a long life, being able to regenerate an electrode and measuring the temperature of an electrode portion, and having a reduced raw material cost. With the goal.

【0010】

[Means for solving problems]

The diamond electrode according to the present invention is characterized in that at least a part of the electrode is formed of a semiconductor diamond film, and the surface of the semiconductor diamond film is chemically modified.

【0011】

In another diamond electrode according to the present invention, undoped diamond particles are fixed to the base material of the electrode, the surface of the undoped diamond particles is formed of a semiconductor diamond film, and the surface of the semiconductor diamond film is chemically modified. It is a feature.

【0012】

Yet another diamond electrode according to the present invention is characterized in that semiconductor diamond particles are embedded in the base material of the electrode and the surface of the semiconductor diamond particles is chemically modified.

【0013】

These semiconductor diamond films are formed by vapor phase synthesis and have 10 borons.¹⁸~ 10²²/cm³ It is doped at the concentration of.

【0014】

Further, it may have a diamond film such that the electrode base material side is a semiconductor diamond film and the surface side is an undoped diamond film having a film thickness of 0.05 to 2 μm.

【0015】

The base material of these electrodes may be a self-supporting diamond film or carbon.

【0016】

Further, the diamond film can be selected from the group consisting of a polycrystalline film, a highly oriented film and a heteroepitaxial film.

【0017】

Further, the surface of the semiconductor diamond film and the semiconductor diamond particles can be selected from the group consisting of (111) crystal planes and (100) crystal planes.

【0018】

The surface of these diamond electrodes can be chemically modified by hydrogenation, oxidation or halogenation. Further, the diamond electrode surface is replaced with one or two or more substituents selected from the group consisting of a hydroxyl group, a cyano group, an amino group, a carboxyl group, a sulfate group, a nitro group, an alkyl group having a molecular weight of 50 or more, and an aroma group. It can also be done by the method of

【0019】

Further, wiring for measuring the electric resistance value may be connected to the semiconductor diamond film and the semiconductor diamond particles.

【0020】

[Action]

As a result of intensive research by the inventor of the present application to solve the above-mentioned problems, diamond is stable to chemical substances and gases, and it is possible to control the characteristics of diamond by chemically modifying the surface thereof. Focusing on this, we found that a highly efficient diamond electrode could be realized. That is, in the present invention, an electrode is manufactured using a semiconductor diamond film or a combination of an undoped diamond film and a semiconductor diamond film, and the surface of the electrode is chemically modified to reduce overvoltage and stabilize for a long time. It is possible to form a high-characteristic diamond electrode that can operate in the Further, the same effect can be obtained by fixing the undoped diamond particles to the base material of the electrode, coating the surface with the semiconductor diamond film, and then chemically modifying the surface.

【0021】

The effect of such chemical modification on the surface of the electrode on the characteristics of the electrode will be described with reference to the energy band structures of FIGS. 2 to 4. FIG. 2 shows the energy band structure when the conventional p-type semiconductor diamond electrode without surface treatment and the electrolyte solution are in contact with each other. As shown in FIG. 2, the oxidation level and the reduction level on the electrolyte solution side are in the forbidden band position on the diamond electrode side, and the reduction level is particularly the upper end of the valence band on the diamond electrode side and the Fermi level. Is between. In addition, in the energy structure on the diamond electrode side that has not been surface-treated, the energy at the upper end of the valence band and the lower end of the conduction band decreases significantly as it approaches the interface with the electrolyte solution side. Charge transfer between is hindered. This causes an increase in overvoltage in electrolysis.

【0022】

Figures 3 and 4 show one example of the energy band structure when the surface of the diamond electrode is chemically modified with a substituent having a negative charge such as a hydroxyl group and the electrolyte solution, and another example. Show each. As shown in FIG. 3, the oxidation level on the electrolyte solution side is in the forbidden band position on the diamond electrode side as in FIG. 2, while the reduction level is in the valence band position on the diamond electrode side. Since this diamond electrode is replaced by a hydroxyl group, the energy structure on the diamond electrode side does not change the energy at the upper end of the valence band and the lower end of the conduction band even at the interface with the electrolyte solution side due to the negative charge of the hydroxyl group. The energy level of a diamond electrode modified with such a negatively charged substituent varies depending on the type of electrolyte solution. For example, as shown in FIG. 4, the energy at the upper end of the valence band and the lower end of the conduction band may increase as the diamond electrode side approaches the interface with the electrolyte solution side. As a result, the oxidation level on the electrolyte solution side is in the forbidden band position as in the positions shown in FIGS. 2 and 3, but the reduction level on the electrolyte solution side is higher than the Fermi level on the diamond electrode side. Further, the upper end of the valence band rises above the Fermi level, so that the reduction level becomes the position of the forbidden band on the diamond electrode side. Therefore, when the chemically modified diamond electrodes shown in FIGS. 3 and 4 are used, the barrier in the movement of holes is eliminated and the overvoltage can be suppressed. Here, when the substituent used for chemical modification is hydrogen, the diamond electrode is hydrophobic, but when it is a hydroxyl group, the diamond electrode is hydrophilic. Therefore, when the electrolyte solution is an aqueous solution, the charge is charged. Is more likely to move. As described above, for the chemical modification of the diamond electrode surface according to the present invention, it is necessary to select the optimum method according to the electrolyte solution and the like.

【0023】

Therefore, the method and type of chemical modification selected in the present invention will be described. The terminal structure of the diamond electrode surface synthesized by the CVD method has a CH structure, and this surface is treated with, for example, a mixed solution of dichromic acid and concentrated sulfuric acid, or with oxygen plasma. As a result, the structure of the terminal CH changes to a structure containing oxygen such as CO. In other cases, it can be chemically modified with various substituents by a known chemical reaction. Generally, chemical modifications include hydrogenation, oxidation, or halogenation, but when used in a hydrophilic solution, one of hydroxyl groups, cyano groups, amino groups, carboxyl groups, sulfate groups, or nitro groups is used. Or terminate with two or more substituents. Further, when a special chemical reaction process is to occur in the electrode, it is preferable to chemically modify the electrode with an alkyl group or an aroma group having a molecular weight of 50 or more. The diamond electrode according to the present invention has the same effect by selecting the type of chemical modification and the like regardless of whether the electrolyte solution is a water-soluble solution, an organic solvent, or a mixed solution of the water-soluble solution and the organic solvent. Is obtained. In general, the organic electrode reaction is greatly affected by the electronic properties of the electrode material, but the use of this electrode may cause a peculiar organic chemical reaction.

【0024】

In addition, when diamond is used for the electrode, diamond is less active than carbon, so even when oxygen is generated from the electrode, the electrode is not consumed by active oxygen, and even if the electrode surface deteriorates, the diamond film Since the surface of the electrode can be cleaned by a method such as chromic acid treatment or oxygen or hydrogen plasma treatment, the electrode can be regenerated by chemically modifying the surface again.

【0025】

The chemical modification is usually performed before the electrode is actually used, but depending on the conditions, it can be performed during the actual use as a diamond electrode. For example, when the nitrite aqueous solution is reduced by electrolysis, the surface of the diamond electrode is oxidized in advance so that the surface of the diamond electrode is nitrated during the electrolysis. In this way, chemical modification suitable for the usage environment can be performed.

【0026】

In the present invention, a semiconductor diamond film or semiconductor diamond particles are used for the electrodes, but as described above, it is known that the semiconductor diamond film can be formed by a vapor phase synthesis method. The diamond electrode according to the present invention does not have to be a uniform semiconductor diamond, and may be a diamond film in which a semiconductor diamond film or an undoped diamond film and a semiconductor diamond film are laminated in one layer or multiple layers, and the distribution is distributed in boron which is a dopant. There may be.

【0027】

When producing a p-type semiconductor diamond film Boron is doped into diamond by the CVD method or the like. The maximum number of boron atoms in this diamond is about 10.²³/cm³ However, if the boron concentration is too high, the crystallinity of diamond is lowered, and conversely, if the boron concentration is too low, the electrical conductivity is reduced and the diamond cannot function as an electrode.

【0028】

Therefore, even in the prior art, it has been reported that the electrode characteristics differ greatly depending on the boron concentration in the semiconductor diamond film. According to this, the electrode characteristics are excellent depending on the number of boron atoms doped and the number of diamond atoms. Ratio B / C is 10^-4Or about 1.8 x 10 per unit volume of diamond¹⁹/cm³ Only if. Doping concentration of boron atom is 1.8 × 10¹⁹/cm³ If it is lower, the electrical resistance of the electrode will increase, causing power loss due to heat generation, and the doping concentration of boron atoms will be 1.8 × 10.¹⁹/cm³ If it is higher, the crystallinity of diamond is lowered, and the original characteristics of diamond are lost.

【0029】

However, the inventor of the present application increases the boron concentration in the semiconductor diamond film by 10 by coating the surface of the semiconductor diamond film with an undoped diamond film having a thickness of 0.05 to 2 μm.¹⁸cm³~ 10²²/cm³It was found that the characteristics of the electrodes are excellent even when expanded to. In particular, in this range, the current tends to flow from the electrode side to the electrolyte side, but does not easily flow in the opposite direction. Therefore, the desired boron concentration for the electrode is 10.¹⁸/cm³~ 10²²/cm³Is. The same effect can be obtained by lowering the doping concentration of boron toward the surface layer of the diamond electrode and forming the outermost surface layer with an undoped diamond film.

【0030】

Further, according to the present invention, it is also possible to embed semiconductor diamond particles in the electrode base material instead of the diamond film and chemically modify the surface thereof. At present, the production cost of diamond particles is lower than that of the diamond film, so that the production cost can be reduced by using the diamond particles.

【0031】

In general, carbon is widely used as an electrode material from batteries to the chemical industry. Therefore, in the present invention, the electrode base material is carbon, and the carbon electrode is coated with a diamond film or the semiconductor diamond particles are embedded. Is possible. As a result, the electrode characteristics can be improved, such as reducing the overvoltage of the carbon electrode and reducing the amount of gas generated. Furthermore, since diamond is composed of carbon atoms, it does not pollute the environment when the electrodes are discarded.

【0032】

Further, when the diamond electrode portion is irradiated with light, electrons are excited from the valence band to the conduction band, so that the electrode function is improved. As shown in Fig. 2 as an example of the energy band structure of a diamond electrode, the energy gap E of diamond is 5.5 eV. Therefore, when the wavelength of the irradiated light is set to about 0.2 μm or less, the energy band shifts from the valence band to the conduction band. Excitation of electrons occurs. However, since various lattice defects and impurities are present in the diamond crystal and these form electron levels in the forbidden band, some effect can be obtained even by irradiating visible light having a wavelength of 0.2 μm or more. be able to.

【0033】

Further, the electrode characteristics of the diamond electrode depend on the crystal plane of diamond. As already described, it is possible to control the crystal plane of diamond, and in the present invention, if the surface of the diamond electrode is composed of (111) crystal plane or (100) crystal plane depending on the type of electrolyte, the electrode efficiency Is improved. Further, the diamond film may exhibit any surface orientation of a polycrystalline film, a highly oriented film or a heteroepitaxial film.

【0034】

Since the electrical resistance value of semiconductor diamond decreases as the temperature rises, this property can be utilized to use a diamond electrode as an electrode and at the same time as a temperature sensor, which is an optimum electrode with reference to the electrode environmental temperature. It becomes possible to drive. For example, since the electrolysis efficiency strongly depends on the temperature, it is necessary to control the temperature of the electrolysis tank in order to control the process of electrolysis. In the present invention, the diamond electrode itself can be used as a temperature sensor by connecting a wiring for measuring the electric resistance value to the semiconductor diamond film and the semiconductor diamond particles, so that the electrode reaction is actually performed instead of the temperature of the electrolysis tank. It is possible to measure the temperature of the electrode surface where the above is occurring. Therefore, more efficient operation control becomes possible, and it is possible to quickly respond to an abnormal situation such as overheating.

【0035】

[Example]

Hereinafter, examples of the diamond electrode according to the present invention will be specifically described in comparison with the comparative examples. First, vapor phase synthesis was performed on a rectangular (width 10 mm, length 20 mm) low-resistance silicon nitride substrate buffed with diamond powder using a microwave CVD device to form a p-type semiconductor diamond film with a thickness of 10 μm. did. This sample is referred to as Comparative Example 1. However, CVD keeps the substrate temperature at 800 to 850 ° C and hydrogen-dilutes diborane (B) so that the concentration with respect to methane 1 to 5%, oxygen 0.1 to 2% and raw material gas is 1 ppm.₂H₆) Was used as the raw material gas, and the gas pressure was kept constant in the range of 30 to 60 Torr for 20 hours.

【0036】

Next, the sample of Comparative Example 1 was subjected to oxygen plasma treatment with a high-frequency plasma generator to oxidize the diamond surface. This sample is referred to as Example 2. However, in the oxygen plasma treatment, the gas pressure of the oxygen gas was set to 0.01 Torr, and the surface treatment was performed for 3 minutes.

【0037】

On the other hand, under the CVD conditions of Comparative Example 1, vapor phase synthesis was performed with the diboran concentration relative to the raw material gas set to 10 ppm to form a p-type semiconductor diamond film with a film pressure of 10 μm, and an undoped diamond film of about 0.1 μm was formed on the surface thereof. Was laminated, and oxygen plasma treatment was performed under the same conditions as the treatment in Example 2 above. This sample is referred to as Example 3.

【0038】

In addition, vapor phase synthesis was performed on a rectangular (width 10 mm, length 20 mm) low-resistance silicon substrate with a (100) crystal plane that was not buffed with diamond powder using a microwave CVD device, and the film thickness was 10 μm. A p-type semiconductor diamond film was formed. However, CVD was carried out under the same conditions as those in Comparative Example 1 and Examples 2 to 3. Next, the p-type semiconductor diamond film was subjected to oxygen plasma treatment in the same manner as in Example 2. This sample is referred to as Example 4.

【0039】

Next, a copper foil lead-out wire having a width of 5 mm and a length of 50 mm was adhered to the back surface of each sample of the comparative example and the example with silver paste, leaving a rectangular portion of 0.5 mm × 15 mm on the surface of the diamond film. The entire part was sealed with epoxy resin. Then, wiring was formed using each of the above samples as an anode and a platinum electrode as a cathode, and the current efficiency and overvoltage were evaluated. For Example 4, only the current efficiency was evaluated. The results are shown in Table 1 below. However, the overvoltage was calculated using a 0.1 M sodium chloride aqueous solution as the electrolyte solution and a calomel electrode as the reference electrode. The current efficiency was estimated from the amount of hydrogen and chlorine generated in the electrodes.

【0040】

In addition, the current efficiency was measured when the electrodes under electrolysis of Comparative Examples 1 and 2 and 3 were irradiated with AM1 light and mercury lamp light. The results are also shown in Table 1 below.

【0041】

[table 1]

【0042】

As shown in Table 1 above, Examples 2 to 4 used diamond electrodes chemically modified by oxidation, and showed higher current efficiency than Comparative Example 1. Further, as shown in Examples 2 and 3, according to the present invention, the overvoltage of the diamond electrode can be reduced to 0.1 V or less by chemical modification. It is also possible to reduce the voltage to 0.05 V or less by selecting the solution, solute and temperature conditions. Further, according to the present invention, the current efficiency is improved, so that the power loss can be reduced. The reason why the current efficiency of Example 3 is superior to that of Example 2 is that the diamond film of Example 3 has a higher boron doping concentration, so that the electrical resistance of the diamond film is reduced, resulting in heat generation. This is because the energy loss due to is small.

【0043】

Since Example 4 was a highly oriented film in which the (100) crystal planes of diamond were regularly arranged even on the surface of the synthesized diamond film, it was higher than the current efficiency of Example 2 formed under the same conditions. The value is shown.

【0044】

Further, by irradiating the electrodes with mercury lamp light, the current efficiency was improved by 3 to 4% in Examples and Comparative Examples. Since AM1 light has the same spectral distribution as sunlight, the power efficiency is not improved as much as the use of mercury lamp light.

【0045】

Next, in each wiring produced under the same conditions as in Comparative Example 1 and Examples 2 and 3, a 0.1 M sodium nitrite aqueous solution was used as the electrolyte solution, and the current efficiency was evaluated at regular intervals. went. Furthermore, the absorption intensity of the CH and NO expansion and contraction vibration bands on the surface of the diamond film was measured by total reflection type Fourier transform infrared spectroscopy. The results are shown in Table 2 below. However, the numerical value shown in the column of absorption intensity is a relative value when the maximum value of absorption intensity is 1.0.

【0046】

[Table 2]

【0047】

As shown in Table 2 above, in Comparative Examples and Examples, the absorption intensity of the CH vibration band decreased with the passage of the electrolysis time, while the absorption intensity of the NO vibration band increased. This is because the diamond electrode surface is C-NO due to the structure of CH during electrolysis.₂It shows that it has changed to. That is, chemical modification can be performed while the diamond electrode functions as an electrode, and as a result, the current efficiency is improved with the passage of electrolysis time.

【0048】

The surface of the diamond electrode of Example 2 used in this experiment was treated with oxygen plasma again and evaluated by the same method as the evaluation in Table 1. As a result, the same value as in Table 1 was shown. This indicates that the diamond electrode of the present invention can be regenerated.

【0049】

Further, when a 0.1 M sodium chloride aqueous solution or a 0.1 M sodium nitrite aqueous solution is used as the electrolyte solution, the overvoltage immediately after the start of electrolysis and the overvoltage after the completion of the 100-hour electrolysis reaction are shown in Example 2. Compared. The sodium chloride aqueous solution was subjected to an electrolysis reaction while maintaining its temperature at 60 ° C. The results are shown in Table 3 below.

【0050】

[Table 3]

【0051】

As shown in Table 3 above, regardless of which electrolyte solution was used, the overvoltage was lower after the completion of the electrolysis reaction than immediately after the start of electrolysis. This is because the surface of the diamond electrode was chemically modified during the electrolysis reaction, as in the evaluation in Table 2.

【0052】

In addition, an electrode was produced so that the diamond electrode could also act as a temperature sensor. FIG. 1 shows an example of a diamond electrode structure having a temperature measuring function. First, as shown in FIG. 1, a p-type semiconductor diamond film 2 is formed on a low-resistance silicon nitride substrate 1 in the same manner as in Comparative Example 1. Next, a metal mask is applied to the surface of the diamond film 2, and a pair of signal extraction electrodes 3a and 3b are formed by a platinum film by a sputtering method. Then, the main wiring 4 for power supply is connected to the back side of the silicon substrate 1, and the electrically sealed wirings 5a and 5b are connected to the signal extraction electrodes 3a and 3b, respectively. Finally, a silicon substrate 1, signal extraction electrodes 3a and 3b, and a part of the main wiring 4 were covered with epoxy resin to form an insulating shield 6, and a diamond electrode 7 was produced. The insulating shield 6 has a function of bringing only the surface of the diamond film into contact with the electrolyte solution.

【0053】

Using this diamond electrode 7, an electrolysis experiment was carried out under the same conditions as in Comparative Example 1 and Examples 2 to 4. With the passage of the electrolysis time, the surface temperature of the diamond electrode 7 increased, and the electrical resistance between the wiring 5a and the wiring 5b decreased by about 2%. This corresponds to an increase in the surface temperature of the electrode by about 30 ° C. That is, by connecting the wiring for measuring the electric resistance value to the diamond electrode, the temperature of the surface of the electrode can be measured, and the operation can be controlled efficiently. For the diamond electrode having the function of measuring the temperature, the shape, material, arrangement of the electrode to be used, the position of the signal extraction electrode, and the like can be freely selected. As the material of the substrate, an electrically insulating material such as metal or silicon nitride can be applied.

【0054】

Further, in order to compare the characteristics of the carbon electrode and the diamond electrode, the carbon rod for the electrode was coated with a diamond film by the following method. First, a carbon paste was thinly coated on the surface of the carbon rod for an electrode, and then diamond powder having an average particle size of 20 μm was applied. This sample is heat-treated in vacuum at 800 to 1000 ° C. Further, vapor phase synthesis is carried out under the same conditions as in Comparative Examples 1 and 2 to 4 by a CVD apparatus to grow a semiconductor diamond film of about 30 μm. I let you. As a result, about 80% of the surface of the carbon rod for the electrode was covered with the diamond film. As a result of evaluating the current efficiency and electrode consumption of the diamond-coated electrode and the untreated carbon electrode by the same method as the evaluation in Table 2, the diamond-coated electrode has a current efficiency as compared with the untreated carbon electrode. Was 58% better and the electrode wear was 80% better. INDUSTRIAL APPLICABILITY According to the present invention, the characteristics of an electrode can be improved by utilizing a conventional carbon electrode which is generally widely used.

【0055】

In addition, in order to compare the effects of various chemical modification methods and types of electrolyte solutions on current efficiency, the current efficiency of the surface treatment methods and electrolyte solutions shown in Table 4 below was evaluated by the same method as in Table 2. went. The results are also shown in Table 4. However, in the evaluation column in the table, indicates that the current efficiency has improved remarkably, indicates that the current efficiency has improved, Δ indicates that there is no change in the current efficiency, and × indicates that the current efficiency has decreased. In addition, hydrogenation indicates that the surface of the diamond electrode was subjected to hydrogen plasma treatment after the same surface treatment as that of the treatment in Example 2.

【0056】

[Table 4]

【0057】

As shown in Table 4 above, the chemical modification of the surface of the diamond electrode improves the current efficiency by selecting the optimum method according to the usage conditions, and the characteristics of the electrode become excellent.

【0058】

[Effect of the invention]

As described in detail above, according to the present invention, since chemically modified diamond is used for the electrode, a diamond electrode having a small overvoltage, a long life, and capable of regenerating the electrode and measuring the temperature of the electrode portion can be obtained. Can be done. Further, according to the present invention, carbon can be used as the base material of the electrode, and diamond particles, which are relatively inexpensive, can be used for the electrode itself, so that a diamond electrode with reduced raw material cost can be obtained. As described above, the present invention makes a great contribution to the fields of chemical industry processes, electrolysis, batteries, photovoltaic power generation, chemical sensors and the like.

[Simple explanation of drawings]

[Figure 1]

It is a schematic perspective view which shows the diamond electrode 7 which concerns on Example of this invention.

[Figure 2]

The energy band structure when the conventional P-type semiconductor diamond electrode and the electrolyte solution are in contact with each other is shown.

[Fig. 3]

An example of an energy band structure when a P-type semiconductor diamond electrode whose surface is chemically modified with a negatively charged substituent and an electrolyte solution is in contact with each other is shown.

[Fig. 4]

Another example of the energy band structure when the P-type semiconductor diamond electrode whose surface is chemically modified with a negatively charged substituent and the electrolyte solution is in contact with each other is shown.

[Explanation of symbols]

1; Silicon substrate 2; Semiconductor diamond film 3a, 3b; Signal extraction electrode 4; Main wiring 5a, 5b; Wiring 6; Insulation shield 7; diamond electrode