KR20060025078A - High temperature pH sensor electrode and pH measurement system using the same - Google Patents

Abstract

The present invention relates to a hydrogen ion sensor electrode capable of measuring pH more accurately at high temperature, and a pH measuring system using the same. More specifically, the internal electrode material of the hydrogen ion sensor electrode is a metal oxide metal on the surface of the metal powder particles The present invention relates to a hydrogen ion sensor electrode and a pH measuring system using the same, which form a metal / metal oxide-integrated composite to measure a more accurate pH over the entire temperature range of a high temperature region.

The high temperature pH sensor electrode and the pH measuring system using the same according to the present invention configured as described above facilitate the electron transfer, lower the impedance to cause a quick electrochemical reaction, a wide temperature range of the high temperature aqueous solution, especially about 150 ℃ The present invention provides a hydrogen ion sensor electrode capable of accurate pH measurement at a relatively low temperature and a pH measuring system using the same.

Hydrogen ion sensor, pH sensor, pH measuring system, oxygen ion conductive ceramic membrane

Description

High-temperature pH sensing electrode and pH measuring system containing same

1 is a schematic diagram schematically showing a hydrogen ion sensor electrode for pH measurement according to the present invention,

2 is a graph showing a result of measuring pH using a sensor electrode and a conventional sensor electrode according to an embodiment of the present invention.

The present invention relates to a hydrogen ion sensor electrode capable of measuring pH more accurately at high temperature, and a pH measuring system using the same. More specifically, the internal electrode material of the hydrogen ion sensor electrode is a metal oxide metal on the surface of the metal powder particles The present invention relates to a hydrogen ion sensor electrode and a pH measuring system using the same, which form a metal / metal oxide-integrated composite to measure a more accurate pH over the entire temperature range of a high temperature region.

Conventionally, various pH electrodes for measuring pH, such as aqueous solution, have been developed. For example, Korean Patent Application No. 1978-1723 discloses a composite electrode for measuring pH, etc., which can measure ions, ORP, pH, etc., and Korean Patent Application No. 1980-3262 discloses pH and pH of a chemical copper plating solution. Disclosed is a main electrode for pH measurement, in which a reducing agent concentration can be converted into a pH value and measured accurately continuously for a long time.

However, the above-described conventional inventions and the like only disclose a pH electrode for measuring pH at a normal temperature.

Meanwhile, the pH (-log [H ⁺ ]) measuring electrode developed for application to high temperature aqueous solution includes hydrogen electrode, palladium-hydrogen (Pd-H) electrode, metal / metal oxide electrode, and oxygen ion conductivity. Metal / metal oxide electrodes based on ceramic films.

First, the electrode reaction and potential of the hydrogen electrode are expressed as follows.

Electrode reaction: 2H ^{+ _{(solution) + 2e - → H 2 (}} Pt)

Potential: E =-(2.303RT / 2F) log ( f _H2 )-(2.303RT / F) pH

Application temperature range for pH measurement of the hydrogen electrode is known to be 25 ~ 300 ℃. However, the electrode is a hydrogen, and the molecule has to be present in solution, the need to know in order to have a restriction that it can only work with a stable system to the reduction by hydrogen, and further calculates the exact potential hydrogen bankrupt capacity (fugacity (f _H2)) It is also not easy to measure, which is disadvantageous in actual use.

Second, the electrode reaction of the palladium-hydrogen (Pd-H) electrode is expressed as follows.

Electrode reaction: H ^{+ (solution) + e - → H (Pd} )

The practical application temperature range of the electrode is known to be 25 to 200 ° C. However, in general, in the measurement of pH of a high temperature aqueous solution, at least 300 ° C. of the applicable temperature is required, the electrode may not be preferably used for measuring a pH of a high temperature aqueous solution because the application temperature range is narrow. Moreover, a more fundamental limitation of the electrode is that the sensor electrode cannot be used as a pH measuring electrode in a solution containing an oxidizing agent such as dissolved oxygen.

Third, in the case of the metal / metal oxide electrode, except for the W / WO ₃ system, there is a disadvantage in that accurate pH cannot be measured because Nernstian pH behavior is not exhibited. On the other hand, the electrode reaction and the potential of the W / WO ₃ system showing the Nernian pH behavior of the metal / metal oxide electrode is expressed as follows.

Electrode reaction: WO ₃ ⁺ 6H + ^{(solution) + 6e - → W + 3H} 2 O

Potential: E = E ^o _{W /} WO3-(2.303RT / F) pH

However, the practical application temperature range of the electrode is known to be 25 to 200 ° C., and thus cannot be preferably used for pH measurement of a high temperature aqueous solution as in the case of the palladium-hydrogen (Pd-H) electrode. In addition, there are disadvantages in that the chemical form of tungsten oxide is very diverse and difficult to use due to its poor durability.

Finally, the metal / metal oxide electrode based on the oxygen ion conductive ceramic film is currently used most because the ceramic film has chemical resistance and thus can be applied to various chemical environments. The yttria-stabilized zirconia (YSZ) sensor electrode (M / MO | YSZ | H ⁺ , H ₂ O) having excellent oxygen ion conductivity and good mechanical strength is most widely used as the ceramic membrane.

The total electrode reaction and potential of the electrode are as follows.

The electrode ^{reaction: MO x + 2 x H +} ( solution) x 2 + e ^- → M x + H ₂ O

Potential: E = E ^o _{M / MO x-} (2.303RT / F) pH

Looking at the total electrode reaction equation and the potential equation, the potential does not seem to have anything to do with the ceramic film. However, the actual measured potential may vary depending on the type of ceramic film. Oxygen ion conduction occurs in the ceramic membrane, and the potential measured only depends on the pH of the solution if the conductivity is high enough. In other words, the potential measured in the ceramic membrane with poor oxygen ion conductivity does not accurately reflect the pH of the solution.

Conventional technologies for metal / metal oxide electrodes based on the oxygen ion conductive ceramic membranes include US Pat. Nos. 4,264,424 and 6,551,478.

The U.S. Patent No. 4,264,424 (GE, USA) relates to a metal / metal oxide hydrogen ion sensor electrode based on an oxygen ion conductive ceramic film. The main components of the ceramic film are zirconium oxide, thorium oxide, Cerium oxide, lanthanum oxide, etc. are used, yttria, scandia, calcia, magnesia, etc., are used as additives, and internal electrodes are also used. A hydrogen ion sensor electrode using copper / copper oxide, iron / ferrous oxide + magnetite, or the like is disclosed as a material.

In addition, U. S. Patent No. 6,551, 478 (U.S. Department of Energy) discloses a sensor electrode consisting of a flexible tube, an oxygen ion conductive ceramic plug located at the end of the tube, and a metal / metal oxide electrode reaction system. In this patent, Teflon is described as the material of the tube, and stabilized zirconia is described as the material of the ceramic plug. In addition, as the electrode reaction system, copper / copper oxide, iron / iron oxide, silver / silver oxide, nickel / nickel oxide, mercury / mercury oxide, and the like are described.

The conventional ceramic membrane-based hydrogen ion sensor electrode described above is the most widely used due to the chemical inactivity of the ceramic membrane due to its applicability to various chemical environments, high precision, and excellent durability.

However, the YSZ membrane-based sensor electrode, which has a relatively high performance among the ceramic membrane-based hydrogen ion sensor electrodes, has the impedance of the sensor electrode at a relatively low temperature range of less than 180 ° C in the temperature range of the high temperature aqueous solution, which is the object of measurement except the Hg / HgO system. Shows a tendency to increase significantly because of this, the sensor electrode does not show the Nernstian pH behavior, and as a result, a large error occurs in the measurement of the pH of the solution and cannot be used preferably. On the other hand, in the Hg / HgO system, which can measure pH more accurately even at a relatively low temperature range due to the relatively wide application temperature range, Hg, which is a material used, is not an environmentally friendly material. .

Thus, the present inventors, since the hydrogen ion sensor electrode, shows the Nernstian pH behavior even at low temperature without using Hg / HgO, the hydrogen ion sensor electrode capable of measuring pH more accurately in the entire temperature range of the high temperature aqueous solution. As a result of intensive studies to provide the present invention, the present invention has been completed by developing a sensor electrode capable of lowering the electrochemical impedance of the sensor electrode by an appropriate method.

Accordingly, an object of the present invention is to solve the problems of the conventional hydrogen ion electrode sensor, so that even without the use of Hg / HgO shows the Nernian pH behavior even at low temperatures of the high temperature aqueous solution to be measured, than in the entire temperature range of the high temperature aqueous solution It is to provide a hydrogen ion sensor electrode capable of accurate pH measurement.

Another object of the present invention is to provide a pH measurement system using the hydrogen ion sensor electrode.

In order to achieve the above object, the present invention;

A hydrogen ion sensor electrode comprising an oxygen ion conductive ceramic film, an electrode material, and a conductive current collector, wherein the electrode material comprises a metal / metal oxide integrated composite having a metal oxide present on the surface of a metal particle. It provides a sensor electrode.

In addition, the present invention;

A hydrogen ion sensor electrode comprising an oxygen ion conductive ceramic film, an electrode material, and a conductive current collector; Reference electrode; In a pH measurement system composed of an electrometer, a metal / metal oxide integrated composite in which a metal oxide is present on the surface of a metal powder particle is used as the electrode material, and the voltage measuring device has a high input impedance. It provides a pH measuring system consisting of a voltage measuring device having a).

In the hydrogen ion sensor electrode according to the present invention, the oxygen ion conductive ceramic tube is at least one main component selected from the group consisting of zirconium (Zr) oxide, thorium (Th) oxide, bismuth (Bi) oxide and cerium (Ce) oxide. And one or more dopants selected from the group consisting of yttrium (Y) oxide, magnesium (Mg) oxide, calcium (Ca) oxide, scandium (Sc) oxide, erbium (Er) oxide, and samarium (Sm) oxide. .

In the hydrogen ion sensor electrode according to the present invention, the main metal of the metal / metal oxide composite is specifically copper, iron, silver, platinum, gold, nickel, cobalt, zinc, tungsten, titanium (Ti), iridium ( Ir), rhodium (Rh), zirconium (Zr), palladium (Pd), tin (Sn), or combinations thereof and alloys thereof.

The electrode material of the hydrogen ion sensor electrode according to the present invention is various kinds of graphite (carbon), carbon fiber (carbon black), carbon nanotube (carbon nanotube), carbon nano to reduce the electrical resistance One or more selected from the group consisting of carbon nanoballs, mixtures thereof, and derivatives thereof may be included as the first additive.

In addition, the electrode material of the hydrogen ion sensor electrode is one selected from the group consisting of various transition metals, platinum, gold, silver, mixtures thereof and alloys thereof, which are not electrochemically reactive and have a large specific surface area in order to reduce electrical resistance. The above may further include a second additive.

In the pH electrode system according to the present invention, the high temperature reference electrode may use one of silver / silver chloride (Ag / AgCl) electrodes, platinum / hydrogen (Pt / H ₂ ) electrodes, and palladium / hydrogen (Pd-H) electrodes. have.

In the pH electrode system according to the present invention, the input impedance of the voltage measuring device for measuring the voltage between the hydrogen ion sensor electrode and the reference electrode is preferably 10 ⁸ ohm or more, more preferably 10 ¹⁰ ohm or more and most preferably It is below 10 ¹² ohms.

Hereinafter, the present invention will be described in more detail.

The present invention can more accurately measure the pH of a solution in a wider temperature range, especially in a relatively low temperature (eg 150 ° C.) range, in high temperature pH measurements such as 100 to 300 ° C., and therefore can be applied over a wide range of temperatures. In providing a pH measuring system, the pH measuring system is composed of an oxygen ion conductive ceramic membrane, an electrode material of a metal / metal oxide integrated composite in which a metal oxide is present on a surface of a metal powder particle, and a conductive current collector, as described above. Hydrogen ion sensor electrode; High temperature reference electrode; And an electrometer with high input impedance.

The oxygen-ion conductive ceramic membrane-based hydrogen ion sensor electrode (M / MO | ceramic membrane | H ⁺ , H ₂ O) has two interfaces with respect to the ceramic membrane and moves oxygen ions into and out of the interface. The following reactions occur inside and outside the interface.

That is, the detailed reaction occurring at the sensor electrode is as follows.

A. Solution-side interface: 2 x H ⁺ (solution) + O ^2- (ceramic membrane) → H ₂ O

B. Inside the ceramic membrane: Oxygen ion transfer

C. tube inside ^{surface: MO x + 2 x e -} → M + O 2- ( ceramic film)

When the three reactions (A to C) are combined, the following overall reaction formula can be obtained.

The electrode ^{reaction: MO x + 2 x H +} ( solution) x 2 + e ^- → M x + H ₂ O

The Nernst equation of the total electrode reaction is as follows.

Potential: E = E ^o _{M / MO x-} (2.303RT / F) pH

Consequently, the pH of the solution can be calculated from the potential measured at the ceramic membrane electrode.

In order for the sensor electrode to show the Nernian pH behavior even at a low temperature, the electrochemical impedance of the sensor electrode should be lowered. The main elements of the sensor electrode impedance are impedance due to oxygen ion movement inside the ceramic film, and impedance due to electrode reaction of the internal electrode material. In order to lower the impedance due to oxygen ion migration even at a low temperature, it may be proposed to reduce the thickness of the ceramic film or to change the type of the ceramic film. As described above, the present invention mainly reduces the impedance of the electrochemical reaction in the tube. The electrode reaction material was improved. As described above, in the present invention, the metal oxide is lowered by using the electrode material of the metal / metal oxide integrated composite present on the surface of the metal powder particles, and as a result, the impedance and the electrochemical reaction rate are inversely proportional to each other. The electrochemical reaction rate of the hydrogen ion sensor electrode was improved.

That is, in the metal / metal oxide system of the conventional ceramic film-based sensor electrode, there are various problems such as lowering the electrode reaction rate by constructing the sensor electrode by appropriately mixing two materials with metal and metal oxide in a ceramic tube. However, the electrode sensor of the present invention configured as described above significantly improved the speed of the electrode reaction.

In more detail, as described above, the improvement of the electrode reaction rate of the hydrogen ion sensor electrode according to the present invention was achieved by two specific configurations as follows.

First, it was achieved by using a metal / metal oxide integrated composite as an electrode material. In the present invention, the metal oxide is basically used a material located on the surface of the metal powder particles. The method of manufacturing a metal / metal oxide integrated composite includes a method of oxidizing a metal surface, a method of attaching a metal oxide to a surface of metal particles, and the like. Metal surface oxidation methods include oxidation in air, oxidation by heat under oxygen atmosphere, chemical oxidation by solution under various chemical conditions, and the like. Physical chemical bonding methods include vacuum deposition, spin coating, pressing, and the like.

Second, in the present invention, the electrode reaction rate was improved by using an additive to facilitate electron transfer. Selected from the group consisting of various kinds of graphite, carbon fiber, carbon black, carbon nanotubes, carbon nanoballs, mixtures thereof, and derivatives thereof to reduce electrical resistance with the additive. One or more of which may be included as the first additive. Alternatively, the second additive may further include one or more selected from the group consisting of various transition metals, platinum, gold, silver, mixtures, and alloys of which are not electrochemically reactive and have a large specific surface area.

The conductive current collector of the hydrogen ion sensor electrode according to the present invention is essentially only a role of electron transfer, but may further participate in the electrode reaction. The conductive current collector is copper, iron, silver, platinum, gold, nickel, cobalt, chromium, zinc, tungsten, titanium (Ti), iridium (Ir), rhodium (Rh), zirconium (Zr), palladium (Pd), carbon , Tin (Sn), metals plated with these, metals surface-treated with them, combinations thereof, and alloys thereof.

Examples of the high temperature reference electrode of the pH measuring system according to the present invention include a silver / silver chloride (Ag / AgCl) electrode, a platinum / hydrogen (Pt / H ₂ ) electrode, and a palladium / hydrogen (Pd-H) electrode. In the case of the silver / silver chloride electrode, it is preferable to take an external reference electrode method because the life is shortened due to the thermal hydrolysis of silver chloride, which is commonly occurring in a high temperature reducing environment.

The voltage between the hydrogen ion sensor and the reference electrode of the pH measurement system can be measured using a suitable electrometer. Since the current amount of the sensor electrode is very small, if more current flows toward the electrometer, the equilibrium reaction of the sensor electrode is impaired, and the measured potential does not accurately reflect the pH of the solution. For this reason, according to the present invention, it is preferable to use an electrometer having a large input impedance so that almost no current flows toward the electrometer. The higher the input impedance of the electrometer for measuring the voltage between the hydrogen ion sensor and the reference electrode according to the present invention, the better, and should be at least 10 ⁸ kHz or more. It is generally more desirable to use an electrometer with a high input impedance of 10 ¹² kHz or more.

In the hydrogen ion sensor electrode according to the present invention configured as described above using a metal / metal oxide integrated composite present in the form of the metal oxide is applied to the surface of the metal as an electrode material, to add an additive to facilitate electron transfer By improving the electrode reaction speed by reducing the impedance, it provides a hydrogen ion sensor electrode capable of accurate pH measurement over a wide temperature range of a high temperature aqueous solution, especially at a relatively low temperature.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The following examples are merely presented to aid the understanding of the present invention, of course, the present invention is not limited to the following examples.

<Example 1>

Ni powder (Alfa, purity = 99.99%, particle size = 5 um) was put in an oven where the temperature was kept constant at 80 ° C., and the surface of Ni particles was partially oxidized under an oxygen atmosphere for at least 6 hours. Ni powder whose surface is oxidized is filled in the bottom of a closed yttria-stabilized zirconia (YSZ) membrane tube at one end of Custom Technology Ceramics (CTC) in the United States, followed by platinum wire (length: 300 mm, diameter 1.0 mm). Was placed in the powder layer. The length, outer diameter and inner diameter of the YSZ (yttria = 8.5 wt%) tube were 220 mm, 8.0 mm and 5.0 mm, respectively. Glass wool was placed on the Ni / NiO integral composite powder layer, and MgO was almost filled to the tube entrance, and the packing density of the material in the tube was increased using a vibrator. The tube was finally closed using a ceramic sealant to prevent the filled material from coming out. The YSZ membrane electrode filled with electrode material was loaded in a properly designed stainless steel body to fix and protect the electrode.

<Example 2>

A 0.01 MB (OH) ₃ aqueous solution was used as the test solution. The solution was placed in an autoclave of high temperature and high pressure, and argon gas purging was performed for 10 hours or more to completely remove the dissolved CO ₂ and oxygen in the solution. The autoclave was loaded with the hydrogen ion sensor electrode of Example 1 and an external Ag / AgCl reference electrode. After measuring the potential of the hydrogen ion sensor electrode at a temperature range of 150 ~ 280 ℃ and calculated the pH of the test solution using the Nernst equation. The voltage between the hydrogen ion sensor electrode and the reference electrode was measured using a Keithley 602 electrometer (input impedance = 10 ¹⁴ mA). The measured pH results are shown in FIG. 2.

<Example 3>

Example 1 except that the Ni / NiO integral composite powder and the carbon nanotubes were mixed at a weight ratio of 100 to 1 before the Ni / NiO integral composite powder was introduced into the YSZ tube, and the mixture was placed at the bottom of the YSZ tube. A hydrogen ion sensor electrode was prepared as described above.

Comparative Example 1

Except for using NiO (Alfa, Purity = 99.99%, Particle Size = 5 um) and NiO (Aldrich, Purity = 99.99%, Particle Size = 10 um) instead of NiO surface treated with NiO In the same manner as in Example 1 to prepare a hydrogen ion sensor electrode. Here, Ni powder and NiO powder were mixed evenly using a mixer at a weight ratio of 1 to 1 before being put into the YSZ tube.

Comparative Example 2

Except that the sensor electrode of Comparative Example 1 was used, the pH was measured by the same conditions and methods as in Example 2, and the results are shown in FIG.

As can be seen in Figure 2, in the temperature range of 180 ~ 280 ℃ both the pH value measured in the sensor electrode of Example 2 and Comparative Example 2 is almost similar to the theoretical pH value. However, at 150 ° C., in Example 2, there is no significant difference from the actual pH, but in Comparative Example 2, a large error occurs. This result shows that when the conventional simple metal / metal oxide mixture is used, the impedance is large at the low temperature of about 150 ° C. of the sensor electrode, and thus an error occurs. When the / metal oxide integrated composite is used, an error does not occur even at a temperature as low as 150 ° C., and thus it can be preferably used in all areas including a relatively low temperature range of a high temperature aqueous solution.

The high temperature pH sensor electrode and the pH measurement system using the same according to the present invention configured as described above facilitates the electron transfer, causing a quick electrochemical reaction by reducing the impedance, so that a wide temperature range of the high temperature aqueous solution, in particular about 150 ℃ The present invention provides a hydrogen ion sensor electrode and a pH measurement system using the same, capable of accurate pH measurement even at relatively low temperatures.

Claims (20)

A hydrogen ion sensor electrode comprising an oxygen ion conductive ceramic film, an electrode material, and a conductive current collector, wherein the electrode material comprises a metal / metal oxide integrated composite having a metal oxide present on the surface of a metal particle. Sensor electrode.  The metal of the metal / metal oxide integrated composite in which the metal oxide is present on the surface of the metal particles is copper, iron, silver, platinum, gold, nickel, cobalt, zinc, tungsten, titanium (Ti), iridium ( Ir), rhodium (Rh), zirconium (Zr), palladium (Pd), tin (Sn), hydrogen ion sensor electrode, characterized in that at least one selected from the group consisting of.  The method of claim 1, wherein the metal oxide of the metal / metal oxide integrated composite in which the metal oxide is present on the surface of the metal particles is copper oxide, iron oxide, silver oxide, platinum oxide, gold oxide, nickel oxide, cobalt oxide, zinc oxide, At least one selected from tungsten oxide, titanium (Ti) oxide, iridium (Ir) oxide, rhodium (Rh) oxide, zirconium (Zr) oxide, tin (Sn) oxide and oxides of aluminum or mixtures of these oxides. Ion sensor electrode.  The hydrogen ion sensor electrode of claim 1, wherein the hydrogen ion sensor electrode further comprises an additive for reducing electrical resistance.  The method of claim 4, wherein the additive is graphite, carbon fiber, carbon black, carbon nanotubes, carbon nanoballs, mixtures thereof. And at least one selected from the group consisting of derivatives thereof as a first additive.  5. The method of claim 4, wherein the additive is added as a second additive at least one selected from the group consisting of various transition metals, platinum, gold, silver, mixtures and alloys thereof, which are not electrochemically reactive and have a large specific surface area. Hydrogen ion sensor electrode characterized in that.  The hydrogen ion sensor electrode of claim 1, wherein a metal oxide thickness of the metal / metal oxide composite on the metal surface is 0.001 to 100 um.  8. The hydrogen ion sensor electrode as claimed in claim 7, wherein the metal oxide thickness of the metal / metal oxide composite on the metal surface is 0.01 to 10 um. The method of claim 1, wherein the oxygen ion conductive ceramic is selected from the group consisting of zirconium (Zr) oxide, thorium (Th) oxide, bismuth (Bi) oxide and cerium (Ce) oxide, yttrium (Y) oxide, magnesium Hydrogen ion sensor, characterized in that the solid electrolyte consisting of one or more dopants selected from the group consisting of (Mg) oxide, calcium (Ca) oxide, scandium (Sc) oxide, erbium (Er) oxide and samarium (Sm) oxide. electrode. The hydrogen ion sensor electrode according to claim 9, wherein the amount of the additive is 3 to 20% by weight. The hydrogen ion sensor electrode according to claim 10, wherein the amount of the additive is 5 to 15% by weight.  The method of claim 1, wherein the conductive current collector is copper, iron, silver, platinum, gold, nickel, cobalt, chromium, zinc, tungsten, titanium (Ti), iridium (Ir), rhodium (Rh), zirconium (Zr) And palladium (Pd), carbon, tin (Sn), metals surface-treated with these, combinations thereof, and alloys thereof.  The method of claim 12, wherein the conductive current collector is selected from the group consisting of copper, iron, silver, platinum, gold, nickel, cobalt, chromium, zinc, tungsten, titanium (Ti), combinations thereof and alloys thereof. Hydrogen ion sensor electrode.  14. The hydrogen ion sensor electrode of claim 13, wherein the conductive current collector is selected from the group consisting of copper, iron, silver, platinum, gold, nickel, combinations thereof, and alloys thereof. i) a hydrogen ion sensor electrode comprising an oxygen ion conductive ceramic film, an electrode material and a conductive current collector; ii) a reference electrode; And iii) a pH measurement system comprising an electrometer, wherein said electrode material uses a metal / metal oxide integrated composite in which metal oxide is present on the surface of a metal particle. 16. The pH measuring system of claim 15, wherein the voltage measuring device comprises a voltage measuring device having a high input impedance. 17. The pH measurement system of claim 16, wherein an input impedance of an electrometer for measuring the voltage between the hydrogen ion sensor and the reference electrode is 10 ⁸ ohm or more. 18. The pH measurement system of claim 17, wherein an input impedance of an electrometer for measuring the voltage between the hydrogen ion sensor and the reference electrode is 10 ¹⁰ ohm or more. 19. The pH measurement system of claim 18, wherein an input impedance of an electrometer for measuring the voltage between the hydrogen ion sensor and the reference electrode is 10 ¹² ohm or more. The pH measuring system of claim 15, wherein the high temperature reference electrode is one of a silver / silver chloride (Ag / AgCl) electrode, a platinum / hydrogen (Pt / H ₂ ) electrode, and a palladium / hydrogen (Pd-H) electrode. .

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