JP7709160B2 - Dissolved hydrogen concentration measuring device, electrode for the dissolved hydrogen concentration measuring device, and method for measuring dissolved hydrogen concentration - Google Patents

Description

The present invention relates to a dissolved hydrogen concentration measuring device that uses an electrochemical measurement method to measure the dissolved hydrogen concentration in a liquid to be measured, such as hydrogen water, an electrode for the dissolved hydrogen concentration measuring device, and a method for measuring the dissolved hydrogen concentration.

In recent years, hydrogen water, which is made by dissolving hydrogen molecules (hydrogen gas) in water, has been attracting attention in various fields. For example, in the health industry, hydrogen water is used as drinking water for maintaining health, as the hydrogen molecules in hydrogen water reduce and remove active oxygen in the body. In the electronics industry, hydrogen water is used as water for washing electronic parts, as it has a cleaning effect. In the medical field, hydrogen water has attracted attention for its efficacy in suppressing neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease, improving diabetes, suppressing oxidative stress, anti-fatigue, anti-cancer, suppressing arteriosclerosis, suppressing drug side effects, suppressing kidney function/kidney transplant damage, suppressing small intestine transplant damage, and suppressing allergic diseases.

In the fields of health and electronics industries, and particularly in the medical field, there is a need to accurately measure the dissolved hydrogen concentration in hydrogen water. In general, hydrogen molecules tend to escape from hydrogen water easily, and the dissolved hydrogen concentration tends to decrease over time, so it is important to measure and understand the dissolved hydrogen concentration in hydrogen water at the time of use.

Gas chromatography (GC) is the most commonly used device for measuring dissolved hydrogen concentration, but this GC has problems in that it is expensive, complicated to operate, and not easy to use. In contrast, a dissolved hydrogen concentration measurement device using electrochemical measurement, which measures the current that flows during the oxidation-reduction reaction of molecules and the potential at the electrode interface, not only does not require large-scale equipment, but is also inexpensive and easy to operate, allowing for accurate measurements. Furthermore, electrochemical measurement allows measurements to be made simply by immersing the electrodes in the solution to be measured, making it possible to perform continuous measurements in real time.

Metal electrodes such as platinum (Pt) have traditionally been used as electrodes for measuring dissolved hydrogen concentration using electrochemical measurement methods, but in order to perform accurate measurements with metal electrodes, they must be pre-treated by polishing each time, making the measurements extremely cumbersome.

If a conductive diamond electrode such as that described in Patent Document 1 is used as the measurement electrode, measurements can be made without performing such pretreatment by polishing.

Patent No. 4324672

However, when electrochemical measurements of hydrogen water (cyclic voltammogram (CV) measurements) were actually performed using a boron-doped diamond electrode (BDD electrode), which is a conductive diamond electrode described in Patent Document 1, as the working electrode, no hydrogen-related peak value could be detected in the response current flowing between the working electrode and the counter electrode. As a result, the dissolved hydrogen concentration could not be measured in the CV measurement using the BDD electrode as the working electrode.

The present invention solves the above-mentioned problems of the conventional technology, and the object of the present invention is to provide a dissolved hydrogen concentration measuring device that is capable of measuring dissolved hydrogen concentration and allows easy pretreatment of the electrodes during measurement, an electrode for the dissolved hydrogen concentration measuring device, and a method for measuring dissolved hydrogen concentration.

According to the present invention, the dissolved hydrogen concentration measuring device includes a working electrode immersed in the liquid to be measured, and a measuring circuit that obtains the dissolved hydrogen concentration in the liquid to be measured by applying a predetermined potential to the working electrode and measuring the response current. The working electrode is an electrode in which the surface of a conductive diamond is modified with platinum.

In this device, a specific potential is applied to the working electrode to measure the response current and obtain the dissolved hydrogen concentration in the solution being measured. The working electrode is an electrode in which the surface of a conductive diamond is modified with platinum, making it possible to measure the dissolved hydrogen concentration with good reproducibility. Furthermore, even if the electrode is not polished before measurement, the dissolved hydrogen concentration can be measured with good stability and reproducibility.

It is preferable that the conductive diamond is a polycrystalline diamond thin film doped with boron, and the platinum is platinum electrodeposited on the surface of the polycrystalline diamond thin film.

It is also preferable that the measurement circuit is configured to include a working electrode that transfers electrons, a reference electrode that serves as a potential reference for the working electrode, and a counter electrode that forms a current circuit with the working electrode, and to linearly sweep the potential difference between the working electrode and the reference electrode to measure the response current that flows between the working electrode and the counter electrode.

It is also preferable that the measurement circuit is configured to apply a potential difference between the working electrode and the reference electrode that is assumed to be the potential difference at which a peak value appears in the response current flowing between the working electrode and the counter electrode, or a potential difference within a predetermined range including this potential difference, to measure the response current.

It is more preferable that the measurement circuit is configured to obtain the dissolved hydrogen concentration in the liquid being measured from the peak value of the measured response current.

Furthermore, it is also preferable that the measurement circuit includes a peak value detection means for detecting the peak value of the measured response current, and a dissolved hydrogen concentration extraction means for determining the dissolved hydrogen concentration using a preset relationship between the peak value detected by the peak value detection means and the dissolved hydrogen concentration.

It is also preferable that the measurement circuit is configured to correct the obtained dissolved hydrogen concentration in the liquid being measured according to the electrical conductivity of the liquid being measured.

In this case, it is more preferable that the measurement circuit is configured to correct the obtained dissolved hydrogen concentration by adding the hydrogen concentration difference to the obtained dissolved hydrogen concentration or by multiplying the hydrogen concentration ratio.

According to the present invention, an electrode for a dissolved hydrogen concentration measuring device is provided, which is used as the working electrode of the above-mentioned dissolved hydrogen concentration measuring device and is formed by modifying the surface of a conductive diamond with platinum.

According to the present invention, the method for measuring the concentration of dissolved hydrogen further involves immersing a working electrode, which is an electrode having a conductive diamond surface modified with platinum, in the liquid to be measured, applying a predetermined potential to the working electrode, and measuring the response current to obtain the concentration of dissolved hydrogen in the liquid to be measured.

It is preferable to use an electrode in which platinum is electrodeposited on the surface of a boron-doped polycrystalline diamond thin film as the working electrode.

It is also preferable to obtain the dissolved hydrogen concentration in the solution to be measured by linearly sweeping the potential difference between the working electrode that receives and exchanges electrons and the reference electrode that serves as the potential standard for the working electrode and measuring the response current that flows between the working electrode and the counter electrode.

It is also preferable to measure the response current by applying a potential difference between the working electrode and the reference electrode that is assumed to be the potential difference at which a peak value appears in the response current flowing between the working electrode and the counter electrode, or a potential difference in a predetermined range including this potential difference.

In this case, it is more preferable to obtain the dissolved hydrogen concentration in the liquid being measured from the peak value of the measured response current.

More specifically, it is also preferable to detect the peak value of the measured response current and determine the dissolved hydrogen concentration using a preset relationship between the detected peak value and the dissolved hydrogen concentration.

It is also preferable to correct the obtained dissolved hydrogen concentration in the liquid being measured according to the electrical conductivity of the liquid being measured.

In this case, it is more preferable to correct the obtained dissolved hydrogen concentration by adding the hydrogen concentration difference to the obtained dissolved hydrogen concentration or by multiplying it by the hydrogen concentration ratio.

According to the present invention, the working electrode is an electrode in which the surface of a conductive diamond is modified with platinum, so that the dissolved hydrogen concentration can be measured with good reproducibility. Furthermore, even if the electrode is not polished before the measurement, the dissolved hydrogen concentration can be measured with good stability and reproducibility.

1 is a block diagram showing an outline of the overall device configuration of a first embodiment of a dissolved hydrogen concentration measuring device of the present invention; 2 is a perspective view showing a schematic configuration example of a working electrode in the dissolved hydrogen concentration measuring device of the present embodiment. FIG. FIG. 1 shows SEM images of a BDD film and a Pt-BDD film. 1 is a characteristic diagram showing the measurement results when CV measurements are performed multiple times in the dissolved hydrogen concentration measuring device of this embodiment. FIG. 1 is a characteristic diagram showing the measurement results when CV measurement is performed by changing the dissolved hydrogen concentration in the dissolved hydrogen concentration measuring device of this embodiment. FIG. 1 is a characteristic diagram showing the measurement results when CV measurement is performed by changing the dissolved hydrogen concentration in the dissolved hydrogen concentration measuring device of this embodiment. FIG. This is a characteristic diagram plotting the peak current density of the response current in CV measurement using the dissolved hydrogen concentration measuring device of this embodiment and the dissolved hydrogen concentration in GC measurement for the test liquid that has been left standing for the same time. FIG. 13 is a characteristic diagram showing the results of CV measurement when a Pt electrode is used as the working electrode. FIG. 13 is a characteristic diagram showing the results of CV measurement when a Pt-BDD electrode is used as the working electrode. 1 is a characteristic diagram showing the results of multiple CV measurements in the dissolved hydrogen concentration measuring device of this embodiment. FIG. 1 is a characteristic diagram plotting the peak current density of the response current versus the number of measurements when multiple CV measurements are performed using the dissolved hydrogen concentration measuring device of this embodiment. 1A and 1B are diagrams showing SEM images of a Pt-BDD film before and after CV measurement in the dissolved hydrogen concentration measuring device of the present embodiment. 4 is a characteristic diagram showing the results of CV measurement using the dissolved hydrogen concentration measuring device of the present embodiment. FIG. FIG. 1 is a characteristic diagram showing the results of CV measurement of a sulfuric acid solution. 1 is a characteristic diagram showing the CV measurement results of an actual sample prepared based on tap water in the dissolved hydrogen concentration measuring device of this embodiment. 1 is a block diagram showing an outline of the overall device configuration of a second embodiment of a dissolved hydrogen concentration measuring device according to the present invention; 1 is a characteristic diagram showing the measurement results when CV measurement was performed by changing the KCl concentration of the KCl aqueous solution in the dissolved hydrogen concentration measuring device of this embodiment. FIG. 1 is a characteristic diagram showing the measurement results when CV measurement is performed by changing the KCl concentration of the KCl aqueous solution in the dissolved hydrogen concentration measuring device of this embodiment. FIG. 1 is a characteristic diagram showing the measurement results when CV measurement was performed by changing the KCl concentration of the KCl aqueous solution in the dissolved hydrogen concentration measuring device of this embodiment. FIG. 1 is a characteristic diagram showing the measurement results when CV measurement was performed by changing the KCl concentration of the KCl aqueous solution in the dissolved hydrogen concentration measuring device of this embodiment. FIG. 1 is a characteristic diagram showing the measurement results when CV measurement is performed by changing the KCl concentration of the KCl aqueous solution in the dissolved hydrogen concentration measuring device of this embodiment. FIG. 1 is a characteristic diagram showing the measurement results when CV measurement was performed by changing the KCl concentration of an aqueous solution derived from tap water using the dissolved hydrogen concentration measuring device of this embodiment. 1 is a characteristic diagram showing the measurement results when CV measurement was performed by changing the KCl concentration of an aqueous solution derived from tap water using the dissolved hydrogen concentration measuring device of this embodiment. 1 is a characteristic diagram showing the measurement results when CV measurement was performed by changing the KCl concentration of an aqueous solution derived from tap water using the dissolved hydrogen concentration measuring device of this embodiment. 1 is a characteristic diagram showing the measurement results when CV measurement was performed by changing the KCl concentration of an aqueous solution derived from tap water using the dissolved hydrogen concentration measuring device of this embodiment. 1 is a characteristic diagram showing the measurement results when CV measurement was performed by changing the KCl concentration of an aqueous solution derived from tap water using the dissolved hydrogen concentration measuring device of this embodiment. This is a characteristic diagram in which the average peak values of the response current obtained by CV measurement using the dissolved hydrogen concentration measuring device of this embodiment and the measured electrical conductivity are plotted for samples of each KCl concentration in a KCl aqueous solution and samples of each KCl concentration in an aqueous solution derived from tap water. FIG. 2 is a characteristic diagram showing the relationship between the KCl concentration and the electrical conductivity of an aqueous KCl solution and an aqueous solution derived from tap water. FIG. 1 is a characteristic diagram corresponding to a formula expressing the relationship between the peak value of the response current and the dissolved hydrogen concentration in an aqueous KCl solution. FIG. 1 is a characteristic diagram of saturated hydrogen concentration versus electrical conductivity in an aqueous KCl solution. FIG. 1 is a characteristic diagram showing the relationship between electrical conductivity and hydrogen concentration difference in a KCl aqueous solution. FIG. 1 is a characteristic diagram showing the relationship between electrical conductivity and hydrogen concentration ratio in a KCl aqueous solution. FIG. 1 is a characteristic diagram showing the relationship between electrical conductivity and saturated hydrogen concentration in an aqueous solution derived from tap water. FIG. 1 is a characteristic diagram showing the relationship between electrical conductivity and hydrogen concentration difference in an aqueous solution derived from tap water. FIG. 1 is a characteristic diagram showing the relationship between electrical conductivity and hydrogen concentration ratio in an aqueous solution derived from tap water.

Figure 1 shows a schematic diagram of the overall device configuration in a first embodiment of the dissolved hydrogen concentration measuring device of the present invention, and Figure 2 shows a schematic diagram of an example of the configuration of the working electrode in the dissolved hydrogen concentration measuring device of Figure 1. This embodiment is an example of a device that measures the dissolved hydrogen concentration of a liquid to be measured without needing to consider electrical conductivity.

In FIG. 1, 10 denotes a cell containing a test solution 11, such as hydrogen water, for which the dissolved hydrogen concentration is to be measured; 12 denotes a working electrode (WE) immersed in the test solution 11; 13 denotes a reference electrode (RE) immersed in the test solution 11 and serving as a reference for determining the potential of the working electrode 12; 14 denotes a counter electrode (CE) immersed in the test solution 11 and forming a current circuit with the working electrode 12; and 15 denotes a measurement circuit electrically connected to the working electrode 12, reference electrode 13, and counter electrode 14.

The measurement circuit 15 includes a potentiostat (constant potential electrolysis device) 15a for performing CV measurements, and an information processing device 15b connected to the potentiostat 15a and consisting of a computer in this embodiment. The potential difference between the working electrode 12 and the reference electrode 13 is linearly swept by the potentiostat 15a, and the information processing device 15b detects the peak value of the response current flowing between the working electrode 12 and the counter electrode 14 to obtain the dissolved hydrogen concentration in the measured solution 11.

The information processing device 15b obtains the dissolved hydrogen concentration in the measurement liquid 11 from the peak value of the detected response current. That is, a correspondence equation or correspondence data between the peak value of the response current and the dissolved hydrogen concentration is set and stored in advance in the information processing device 15b, and when a peak value is detected, the dissolved hydrogen concentration can be obtained from this correspondence equation or correspondence data. As a mere example, the correspondence equation is expressed as _Hcon = a x _Apeak + b. Here, _Hcon is the dissolved hydrogen concentration, _Apeak is the peak value of the response current, and a and b are constants.

In this embodiment, the working electrode 12 is a conductive diamond electrode modified with platinum (Pt), the reference electrode 13 is Ag/AgCl, and the counter electrode 14 is platinum (Pt).

As shown in FIG. 2, the working electrode 12 is formed by depositing a conductive diamond film, a boron-doped diamond (BDD) film 12b, on a silicon substrate 12a, and modifying the surface of the BDD film 12b with platinum (Pt) 12c by electrodeposition.

The BDD film 12b was formed, for example, by polishing the mirror side of the silicon wafer with a polishing pad with diamond powder, ultrasonically cleaning with methanol, and then drying, and then supplying hydrogen gas, a carbon source, and a boron source using microwave plasma chemical vapor deposition (microwave plasma CVD). As a mere example, the plasma output was 5000 W, and the film formation time was 6 hours.

The modification with platinum (Pt) was performed by reducing hexachloroplatinic acid (H ₂ PtCl ₆ ) by chronoamperometry, and platinum 12c was electrodeposited on the surface of the BDD film 12b. Here, the working electrode was the BDD film, the counter electrode was platinum (Pt), and the reference electrode was Ag/AgCl. The solution was 1 mM H ₂ PtCl ₆ prepared using 0.5 M sulfuric acid (H ₂ SO ₄ ). The applied voltage was -0.3 V, and the application time was 150 seconds.

Figure 3 shows SEM images of the deposited BDD film and the Pt-BDD film modified with platinum (Pt). Figure (A) shows the BDD film, and Figure (B) shows the Pt-BDD film, both at a magnification of 10,000x. As shown in Figure (B), the BDD film is modified with Pt, which looks like white particles.

Various studies were conducted on the dissolved hydrogen concentration measuring device of this embodiment, as described below.

First, we investigated the reproducibility of CV measurements and the measurability of dissolved hydrogen concentration.

A working electrode 12 having a Pt-BDD film 12b as shown in Figure 2 was prepared, and CV measurements were performed using the device shown in Figure 1. The reference electrode 13 was Ag/AgCl, and the counter electrode 14 was Pt. For pretreatment, chronoamperometry was performed using 0.1 M KCl (potassium chloride) with an applied voltage of 0.6 V and an application time of 30 seconds. The working electrode 12 was not polished. The liquid to be measured was hydrogen water prepared by filling a container containing 0.1 M KCl solution with hydrogen gas at high pressure. Hydrogen gas was obtained using a hydrogen filling machine DAYS (registered trademark) manufactured by Doctor's Man Co., Ltd. The applied voltage was swept from -6 V to +0.2 V in the CV measurement, and the sweep speed was 100 mV/s.

The reproducibility was investigated by performing CV measurements three times (1st to 3rd). Figure 4 shows a voltammogram, which is the result of the CV measurements. The horizontal axis is the potential (V) of the working electrode 12 with respect to the reference electrode 13, and the vertical axis is the current density (μA/cm ² ) of the current between the working electrode 12 and the counter electrode 14. As can be seen from the figure, good reproducibility was obtained in the three CV measurements. As a result, it can be seen that the configuration of this embodiment (using the working electrode 12 having the Pt-BDD film 12b) makes it possible to perform CV measurement of hydrogen water.

Regarding the possibility of measuring the dissolved hydrogen concentration, the dependence of the CV measurement on the dissolved hydrogen concentration was investigated. The dissolved hydrogen concentration was changed by opening the lid of a container of the liquid to be measured, which was filled with hydrogen gas, and allowing it to stand in the air for a period of time (0 minutes, 30 minutes, 60 minutes, 90 minutes, 120 minutes). Figure 5 shows the measurement results. The horizontal and vertical axes are the same as those in Figure 4. As can be seen from the figure, as the dissolved hydrogen concentration decreases over time, the peak current density of the response current also decreases. Therefore, it can be seen that the configuration of this embodiment (using a working electrode 12 having a Pt-BDD film 12b) makes it possible to measure the dissolved hydrogen concentration.

Next, the correspondence between the peak current density of the response current measured by CV measurement and the dissolved hydrogen concentration measured by gas chromatography (GC) was examined for the dissolved hydrogen concentration measuring device of this embodiment.

As in the previous case, the test liquid was filled with hydrogen gas, the lid of the container was opened, and the liquid was left in the air for a certain period of time (5 minutes, 30 minutes, 60 minutes, 90 minutes, 120 minutes), after which CV measurements were performed using the dissolved hydrogen concentration measuring device of this embodiment and dissolved hydrogen concentration measurements were performed using GC. Figure 6 shows the results of CV measurements using the dissolved hydrogen concentration measuring device of this embodiment. The horizontal and vertical axes are the same as those in Figure 4.

The equipment used for the GC measurements was a TRIlyzer mBA-3000 manufactured by Taiyo Co., Ltd., with a semiconductor gas sensor as the detector, a packed column as the column, synthetic air as the carrier gas, and 1 mL of injection volume (25° C.). The results of the dissolved hydrogen concentration measurements by this GC are shown in Table 1.

7 is a characteristic diagram plotting the peak current density of the response current in the CV measurement by the dissolved hydrogen concentration measuring device of this embodiment and the dissolved hydrogen concentration in the GC measurement for the same measurement time (same dissolved hydrogen concentration). The horizontal axis is the dissolved hydrogen concentration (ppm), and the vertical axis is the peak current density of the response current (μA/cm ² ). It can be seen from the figure that the calibration curve of the peak current density of the response current in the CV measurement and the dissolved hydrogen concentration in the GC measurement is a straight line, and it is possible to measure the dissolved hydrogen concentration by the CV measurement. The approximate equation for this calibration curve is the peak current density of the response current (μA/cm ² )=130×dissolved hydrogen concentration (ppm)−136, which converts to the dissolved hydrogen concentration (ppm)=0.0077×peak current density of the response current (μA/cm ² )+1.05. Furthermore, the peak current density (μA/ ^cm2 ) of the electrode in this measurement can be converted to 1.5×peak value (μA), and when converted to a peak value (μA), the dissolved hydrogen concentration (ppm) is 0.01155×peak value of response current (μA)+1.05. This corresponds to the above-mentioned correspondence equation _Hcon =a× _Apeak +b, where a=0.01155 and b=1.05. If the peak value _Apeak of the response current is obtained from this equation, the dissolved hydrogen concentration _Hcon can be calculated.

Next, we investigated whether pre-polishing treatment for CV measurement is necessary for the working electrode 12 of the dissolved hydrogen concentration measuring device of this embodiment.

Figure 8 shows the results of four CV measurements (1st to 4th) when a Pt electrode was used as the working electrode as in the conventional technology, and Figure 9 shows the results of three CV measurements (1st to 3rd) when a Pt-BDD electrode was used as in this embodiment. The horizontal and vertical axes are the same as in Figure 4. In both the Pt and Pt-BDD electrodes, polishing was not performed as a pretreatment process.

When a Pt electrode is used as the working electrode, the peak current density of the response current decreases with each measurement, as shown in Figure 8. However, when a Pt-BDD electrode is used as the working electrode, the peak current density of the response current does not change significantly even with multiple measurements, as shown in Figure 9, and it was confirmed that the measurement is stable and reproducible. This means that while a Pt electrode requires pretreatment by polishing, a Pt-BDD electrode does not require pretreatment by polishing.

Next, we investigated the repeatability and durability of the working electrode 12 in the dissolved hydrogen concentration measuring device of this embodiment.

Fig. 10 shows the results of 28 CV measurements (1 to 28) when the same working electrode 12 was used in the dissolved hydrogen concentration measuring device of this embodiment. The horizontal and vertical axes are the same as those in Fig. 4. Fig. 11 is a plot of the peak current density of the response current versus the number of measurements in 28 CV measurements. In this figure, the horizontal axis represents the number of measurements, and the vertical axis represents the current density (μA/cm ² ) of the current between the working electrode 12 and the counter electrode 14. The measured solution was prepared for each measurement.

As shown in Figure 10, good reproducibility was obtained in 28 CV measurements. Also, as shown in Figure 11, even when CV measurements were repeated using the same working electrode, the peak current density of the response current did not decrease overall, although there was some variation.

Figure 12 shows SEM images of the Pt-BDD film before and after 28 CV measurements. (A) is before the CV measurement, and (B) is after 28 CV measurements, both at a magnification of 4000x. As shown in (B), the amount of Pt modified on the Pt-BDD film has decreased somewhat, but the electrode itself has not deteriorated and is stable.

Next, we investigated the variation in peak current density of the response current that occurred in the durability test described above.

First, CV and GC measurements were performed on multiple samples of hydrogen water produced under the same conditions to measure the dissolved hydrogen concentration. Figure 13 shows the results of five CV measurements (1st to 5th) made using the dissolved hydrogen concentration measuring device of this embodiment. The horizontal and vertical axes are the same as those in Figure 4.

The equipment used for the GC measurements was a TRIlyzer mBA-3000 manufactured by Taiyo Co., Ltd., with a semiconductor gas sensor as the detector, a packed column as the column, synthetic air as the carrier gas, and 1 mL of injection volume (25° C.). The results of the dissolved hydrogen concentration measurements by this GC are shown in Table 2.

On the other hand, a sulfuric acid solution (0.1 M KCl and 1 mM H ₂ SO ₄ ) was used as the test solution, and CV measurements were performed repeatedly. When sulfuric acid was subjected to CV measurement, a hydrogen peak could be observed, just as in the case of hydrogen water. The concentration of sulfuric acid was kept constant at 1 mM. Figure 14 shows the results of 30 CV measurements (1 to 30) of this sulfuric acid solution. The horizontal and vertical axes are the same as those in Figure 4. It can be seen from this figure that the CV measurement results are all consistent over the 30 consecutive measurements.

From Figure 13, Table 2, and Figure 14, it was inferred that the variation in the peak current density of the response current was not due to the accuracy of the working electrode, but due to the variation in the dissolved hydrogen in the hydrogen water produced. As a result, the durability of the working electrode 12 made of Pt-BDD was proven.

In the above study, KCl was added as an electrolyte to make the hydrogen water conductive. However, most commercially available hydrogen water is made by adding hydrogen to tap water, so CV measurements were performed on actual samples of hydrogen water made from tap water.

FIG. 15 shows the results of CV measurement of an actual sample made from tap water, and shows the peak current density of the response current in the CV measurement when 0.1 M KCl is added and when no KCl is added. In the figure, the horizontal axis is the number of measurements, and the vertical axis is the peak current density of the response current (μA/cm ² ). As can be seen from the figure, when no KCl is added and there is a small amount of electrolyte, the peak current density of the response current decreases, but reproducibility was obtained after five measurements. As a result, it was found that CV measurement is possible with an actual sample made from tap water, and the dissolved hydrogen concentration can be measured without preparing the measured liquid.

As described above, the dissolved hydrogen concentration measuring device of this embodiment uses a Pt-BDD electrode as the working electrode to detect the peak current density of the response current by CV measurement to obtain the dissolved hydrogen concentration in the measured liquid, making it possible to measure the dissolved hydrogen concentration with good reproducibility by electrochemical measurement. In addition, because a Pt-BDD electrode is used, there is no need to polish the electrode before measurement, and the dissolved hydrogen concentration can be measured stably and with high sensitivity. In addition, the Pt-BDD electrode has been confirmed to have good stability and durability when used for repeated measurements.

The dissolved hydrogen concentration measuring device of this embodiment is suitable for use in measuring the dissolved hydrogen concentration of a liquid to be measured, where electrical conductivity does not need to be taken into consideration. That is, when measuring hydrogen water made from Japanese tap water, if a calibration curve is obtained for the hydrogen concentration and the peak value (or peak current density) of the response current based on average tap water (for example, tap water with an electrical conductivity of about 10 mS/m), there is no need to consider electrical conductivity. This is the case, for example, when tap water, mineral water, blood, infusions, dialysis water, etc. are used as the liquid to be measured.

Figure 16 shows a schematic diagram of the overall device configuration of a second embodiment of the dissolved hydrogen concentration measuring device of the present invention. This embodiment is an example of a device that measures the dissolved hydrogen concentration of a liquid to be measured, in which electrical conductivity must be taken into consideration.

In FIG. 16, 110 denotes a cell containing a test liquid 111, such as hydrogen water, for which the dissolved hydrogen concentration is to be measured; 112 denotes a working electrode (WE) immersed in the test liquid 111; 113 denotes a reference electrode (RE) immersed in the test liquid 111 and used as a reference for determining the potential of the working electrode 112; 114 denotes a counter electrode (CE) immersed in the test liquid 111 and forming a current circuit with the working electrode 112; and 115 denotes a measurement circuit electrically connected to the working electrode 112, reference electrode 113, and counter electrode 114. Also, 116 denotes a selection switch connected to the measurement circuit 115 for selecting the expected electrical conductivity value of the test liquid 111. The selection switch 116 is a contact changeover switch, volume, or digital switch for selecting the electrical conductivity value in an analog or digital manner.

The measurement circuit 115 includes a potentiostat (constant potential electrolysis device) 115a for performing CV measurements, and an information processing device 115b connected to the potentiostat 115a and consisting of a computer in this embodiment. The selection switch 116 is connected to the information processing device 115b. The potential difference between the working electrode 112 and the reference electrode 113 is linearly swept by the potentiostat 115a, and the peak value of the response current flowing between the working electrode 112 and the counter electrode 114 is detected by the information processing device 115b, and the dissolved hydrogen concentration in the measurement solution 111 is obtained from the peak value. In this case, the dissolved hydrogen concentration is corrected according to the electrical conductivity value specified by the selection switch 116.

The information processing device 115b obtains the dissolved hydrogen concentration in the liquid to be measured 111 from the peak value of the detected response current and the electrical conductivity specified by the selection switch 116. That is, the information processing device 115b is set with multiple electrical conductivity values of the liquid to be measured that have been obtained in advance, and one electrical conductivity value is specified by input from the selection switch 116. When calculating the dissolved hydrogen concentration from the peak value of the response current, the dissolved hydrogen concentration is corrected by this specified electrical conductivity value. That is, there is a linear correspondence between the electrical conductivity and the peak value of the response current, and the peak value of the response current is affected by the electrical conductivity of the liquid to be measured. For this reason, in this embodiment, the dissolved hydrogen concentration calculated from the peak value of the response current is corrected according to the electrical conductivity to eliminate this influence.

The information processing device 115b has a correspondence equation or correspondence data between the peak value of the response current and the dissolved hydrogen concentration set in advance and stored, and when the peak value is detected, the dissolved hydrogen concentration can be obtained from this correspondence equation or correspondence data. The obtained dissolved hydrogen concentration is corrected based on the electrical conductivity to obtain the final dissolved hydrogen concentration. As a mere example, the correspondence equation between the peak value of the response current and the dissolved hydrogen concentration is expressed as H _con = a x A _peak + b, and when electrical conductivity is corrected, it is expressed as H _con = a x A _peak + b + c or H _con = (a x A _peak + b) x d. Here, H _con is the dissolved hydrogen concentration, A _peak is the peak value of the response current, a and b are constants, c is the hydrogen concentration difference when correction is performed by addition, and d is the hydrogen concentration ratio when correction is performed by multiplication.

In this embodiment, the working electrode 112 is a conductive diamond electrode modified with platinum (Pt), the reference electrode 113 is Ag/AgCl, and the counter electrode 114 is platinum (Pt).

The configuration and manufacturing method of the working electrode 112 are similar to those of the working electrode 12 shown in FIG. 2 in the first embodiment, so a detailed description is omitted.

In this embodiment, in order to examine how the peak value of the response current in the CV measurement should be corrected according to the electrical conductivity of the measured solution, first, samples of KCl aqueous solutions with various KCl concentrations were prepared, as well as samples of aqueous solutions obtained by preparing tap water with KCl (hereinafter, aqueous solutions derived from tap water), and the electrical conductivity of these samples was measured.

The electrical conductivity of the samples was measured using a compact electrical conductivity meter, LAQUAtwin, manufactured by Horiba, Ltd. This electrical conductivity meter immerses an electrical conductivity cell with a pair of current-carrying electrodes in the liquid being measured, passes a current through it, measures the resistance, and determines the electrical conductivity.

The electrical conductivity measured for samples with various KCl concentrations using KCl aqueous solutions is shown in Table 3, and the electrical conductivity measured for samples with various KCl concentrations using aqueous solutions derived from tap water is shown in Table 4. In Table 4, data with a KCl concentration of 0 is for cases where no KCl was added and only tap water was used.

For each of these samples with various KCl concentrations, CV measurements were repeatedly performed using the dissolved hydrogen concentration measuring device of this embodiment. Figure 17 shows the results of four measurements (1st to 4th) of a sample with a KCl concentration of 1 mM using a KCl aqueous solution, Figure 18 shows the results of three measurements (1st to 3rd) of a sample with a KCl concentration of 2.5 mM using a KCl aqueous solution, Figure 19 shows the results of five measurements (1st to 5th) of a sample with a KCl concentration of 5 mM using a KCl aqueous solution, Figure 20 shows the results of nine measurements (1st to 9th) of a sample with a KCl concentration of 7.5 mM using a KCl aqueous solution, and Figure 21 shows the results of nine measurements (1st to 9th) of a sample with a KCl concentration of 10 mM using a KCl aqueous solution. FIG. 22 shows the results of 10 measurements (1st to 10th) of a sample with a KCl concentration of 1 mM made from an aqueous solution derived from tap water, FIG. 23 shows the results of 12 measurements (1st to 12th) of a sample with a KCl concentration of 2.5 mM made from an aqueous solution derived from tap water, FIG. 24 shows the results of 16 measurements (1st to 16th) of a sample with a KCl concentration of 5 mM made from an aqueous solution derived from tap water, FIG. 25 shows the results of 14 measurements (1st to 14th) of a sample with a KCl concentration of 7.5 mM made from an aqueous solution derived from tap water, and FIG. 26 shows the results of 11 measurements (1st to 11th) of a sample with a KCl concentration of 10 mM made from an aqueous solution derived from tap water. In these figures, the horizontal axis shows the potential (V) of the working electrode 12 relative to the reference electrode 13, and the vertical axis shows the current (μA) between the working electrode 12 and the counter electrode 14.

27 is a characteristic diagram plotting the average value of the peak value of the response current obtained by performing CV measurement on samples of each KCl concentration using a KCl aqueous solution and samples of each KCl concentration using an aqueous solution derived from tap water, and the measured value of the electrical conductivity. The horizontal axis is electrical conductivity (mS/m), and the vertical axis is the peak value (peak current value) (μA) of the response current, where A is the sample using a KCl aqueous solution, and B is the sample using an aqueous solution derived from tap water. From the figure, the calibration curve of the peak value of the response current measured by CV measurement and the electrical conductivity is on a straight line. The approximate equation of this calibration curve is the peak value of the response current (μA) = 0.2759 × electrical conductivity (mS/m) + 31.851 for the KCl aqueous solution, and when the peak value of the response current is converted to a current density, the peak current density of the response current (μA/cm ² ) = 0.414 × electrical conductivity (mS/m) + 47.777. For the aqueous solution derived from tap water, the peak value of the response current (μA) = 0.2499 × electrical conductivity (mS/m) + 34.932, and when the peak value of the response current is converted to a current density, the peak current density of the response current (μA/cm ² ) = 0.375 × electrical conductivity (mS/m) + 52.398.

Figure 28 shows the relationship between the KCl concentration and electrical conductivity of a KCl aqueous solution and an aqueous solution derived from tap water based on Tables 3 and 4. The horizontal axis is KCl (mM), and the vertical axis is electrical conductivity (mS/m). The electrical conductivity of a KCl aqueous solution generally indicates linearity at zero concentration, with "approximately 0", and the characteristics shown in Figure 28 also show the electrical conductivity of the KCl aqueous solution as "approximately 0". In addition, in an aqueous solution derived from tap water, when the KCl concentration is about 1 mM, the electrical conductivity is influenced by the tap water, but when the KCl concentration is 2.5 mM or more (electrical conductivity is 50 mS/m or more), the electrical conductivity is mostly based on KCl.

Next, we will actually consider how to correct the peak value of the response current in CV measurement according to the electrical conductivity of the measured liquid.

27, the peak value of the response current (μA) = 0.2759 × electrical conductivity (mS/m) + 31.851 is obtained, and converting from the relationship of current density (μA/ ^cm2 ) = 1.5 × current (μA), the peak current density of the response current (μA/ ^cm2 ) = 0.414 × electrical conductivity (mS/m) + 47.777 is obtained. In reality, the maximum dissolved amount of dissolved hydrogen is not the same depending on the KCl concentration, but it is assumed that the maximum dissolved concentration of tap water in the atmosphere is 1.6 ppm for the calculation.

Furthermore, from the relationship between the peak value of the response current and the dissolved hydrogen concentration described in the first embodiment, the following equation can be obtained: Dissolved hydrogen concentration (ppm) = 0.0077 x peak current density of the response current (μA/ ^cm2 ) + 1.05. Figure 29 shows the relationship between the peak value of the response current and the dissolved hydrogen concentration, which corresponds to this equation. The horizontal axis is the peak value of the response current (μA), and the vertical axis is the dissolved hydrogen concentration (ppm).

As mentioned above, the electrical conductivity of tap water alone is 16.7 mS/m, the maximum dissolved hydrogen concentration in the atmosphere when tap water is used is 1.6 ppm, and the peak value of the response current is Peak response current (μA) = (1.6 - 1.05) / (0.0077 x 1.5) = 47.62 μA. The measured value is Peak response current (μA) = 0.2759 x electrical conductivity (mS/m) + 31.851 = 0.2759 x 16.7 + 31.851 = 36.46 μA.

There is a difference of approximately 11 μA between the calculated value and the measured value. When this 11 μA is converted to dissolved hydrogen concentration, it becomes Dissolved hydrogen concentration difference (ppm) = 0.0077 x 1.5 x Current peak value (μA) = 0.0077 x 1.5 x 11 = 0.13 ppm. Whether this difference is within the acceptable range or not seems to depend on the application, and electrical conductivity correction may be necessary depending on the application of the aqueous solution being measured.

The electrical conductivity of tap water in Japan is approximately 5 to 20 (mS/m). The peak value of the response current, the current density of the peak value (peak current density), and the dissolved hydrogen concentration are shown in Table 5.
From Table 5, the difference in the calculated dissolved hydrogen concentration is only about 0.05 ppm, which is within the margin of error. Therefore, if hydrogen water from tap water in Japan is measured, the effect of electrical conductivity on the measurement results can be ignored if a calibration curve is obtained based on hydrogen concentration and peak value (or peak current density) of the response current using standard water with an electrical conductivity of about 10 mS/m as a reference. When mineral water, blood, infusion, dialysis water, etc. are used as the measured liquid in addition to tap water, electrical conductivity can be ignored if a standard calibration curve is obtained for these main measured liquids.

28, when measuring in a wide range of electrical conductivity from 0 to 150 mS/m, it is desirable to perform a correction. Here, the saturated hydrogen concentration at an electrical conductivity of 16.4 mS/m is 1.6 ppm, and from the relationship between the peak current density value at a current density of 150 μA/cm ² (current value 100 μA) of the peak value of the response current and the dissolved hydrogen concentration, the saturated concentration is: Dissolved hydrogen concentration (ppm) = 0.0077 × current density (μA/cm ² ) + 1.05 = 0.0077 × 150 + 1.05 = 2.20 (ppm). The electrical conductivity at the peak value of 100 μA is calculated by converting the peak value of the response current (μA) = 0.2759 × electrical conductivity (mS/m) + 31.851 to electrical conductivity (mS/m) = (peak value (μA) - 31.851)/0.2759 = (100 - 31.851)/0.2759 = 247 (mS/m). FIG. 30 shows the characteristics of the saturated hydrogen concentration versus electrical conductivity, where the saturated hydrogen concentration is 1.6 ppm when the electrical conductivity is 16.4 mS/m, and the saturated hydrogen concentration is 2.2 ppm when the electrical conductivity is 247 mS/m. In the figure, the horizontal axis is electrical conductivity (mS/m) and the vertical axis is saturated hydrogen concentration (ppm).

From the figure, it can be seen that the formula: calculated saturation hydrogen concentration (ppm) = 0.0026 × electrical conductivity (mS/m) + 1.5573 holds. This result is summarized in Table 6 along with the measured value results. In Table 6, the calculated saturation hydrogen concentration is calculated as calculated saturation hydrogen concentration (ppm) = 0.0026 × electrical conductivity (mS/m) + 1.5573, the peak value of the response current is calculated as peak value of the response current (μA) = 0.2759 × electrical conductivity (mS/m) + 31.851, and the dissolved hydrogen concentration is calculated as dissolved hydrogen concentration (ppm) = 0.0077 × 1.5 × current peak value (μA) + 1.05. In addition, the difference between the calculated saturated hydrogen concentration (ppm) and the measured calculated saturated hydrogen concentration (ppm) is the hydrogen concentration difference (ppm), which is given by hydrogen concentration difference (ppm) = -0.0006 x electrical conductivity (mS/m) + 0.1394.

Figure 31 shows the relationship between electrical conductivity (mS/m) and hydrogen concentration difference (ppm) in Table 6. In the figure, the horizontal axis is electrical conductivity (mS/m) and the vertical axis is hydrogen concentration difference (ppm). Correction based on electrical conductivity can be performed by adding the hydrogen concentration difference shown in the figure to the dissolved hydrogen concentration calculated from the peak value of the response current.

In other words, the corrected calculated hydrogen concentration can be calculated as follows: Corrected calculated hydrogen concentration (ppm) = 0.0077 x 1.5 x current peak value (μA) + 1.05 - (0.0006 x electrical conductivity (mS/m)) + 0.1394 = 0.0077 x 1.5 x current peak value (μA) - 0.0006 x electrical conductivity (mS/m) + 1.1894.

When the corrected calculated hydrogen concentration is calculated using this formula, it is as shown in Table 7.

As can be seen from Table 7, the above correction method results in an error of about 1%, but the dissolved hydrogen concentration is almost the same.

Incidentally, when the corrected calculated hydrogen concentration is obtained by multiplication correction instead of additive correction as described above, it is as shown in Table 8. In Table 8, the calculated saturated hydrogen concentration is calculated by calculated saturated hydrogen concentration (ppm) = 0.0026 x electrical conductivity (mS/m) + 1.5573, the peak value of the response current is calculated by peak value of the response current (μA) = 0.2759 x electrical conductivity (mS/m) + 31.851, and the dissolved hydrogen concentration is calculated by dissolved hydrogen concentration (ppm) = 0.0077 x 1.5 x current peak value (μA) + 1.05. The ratio of the calculated saturated hydrogen concentration (ppm) to the measured calculated saturated hydrogen concentration (ppm) is the hydrogen concentration ratio, which is given by hydrogen concentration ratio = calculated saturated hydrogen concentration (ppm) / measured calculated saturated hydrogen concentration (ppm).

Figure 32 shows the relationship between electrical conductivity (mS/m) and hydrogen concentration ratio (saturation/measurement) in Table 8. In this figure, the horizontal axis is electrical conductivity (mS/m) and the vertical axis is hydrogen concentration ratio (saturation/measurement). The hydrogen concentration ratio (saturation/measurement) is a correction coefficient, and correction based on electrical conductivity can be performed by multiplying the dissolved hydrogen concentration calculated from the peak value of the response current by the water hydrogen concentration ratio (saturation/measurement) shown in the figure, i.e., the correction coefficient.

From Figure 32, the relationship of correction coefficient = -0.0005 x electrical conductivity (mS/m) + 1.0946 holds, so the corrected calculated hydrogen concentration can be calculated as corrected calculated hydrogen concentration (ppm) = (0.0077 x 1.5 x current peak value (μA) + 1.05) x (-0.0005 x electrical conductivity (mS/m) + 1.0946).

When the corrected calculated hydrogen concentration is calculated using this formula, it is as shown in Table 9.

As can be seen from Table 9, this correction method results in an error of about 1%, but the dissolved hydrogen concentration is approximately the same.

27, the peak value of the response current (μA) = 0.2499 × electrical conductivity (mS/m) + 34.932 is obtained, and by converting from the relationship of current density (μA/cm ² ) = 1.5 × current (μA), the peak current density of the response current (μA/cm ² ) = 0.3749 × electrical conductivity (mS/m) + 52.398 is obtained. In reality, the maximum dissolved amount of dissolved hydrogen is not the same depending on the KCl concentration, but it is assumed that the maximum dissolved concentration of tap water in the atmosphere is 1.6 ppm for calculation.

Furthermore, from the relationship between the peak value of the response current and the dissolved hydrogen concentration described in the first embodiment, the following equation is obtained: dissolved hydrogen concentration (ppm)=0.0077×peak current density of response current (μA/cm ² )+1.05, as shown in FIG.

As mentioned above, the electrical conductivity of tap water alone is 16.7 mS/m, the maximum dissolved hydrogen concentration in the atmosphere when tap water is used is 1.6 ppm, and the peak value of the response current is Peak response current (μA) = (1.6 - 1.05) / (0.0077 x 1.5) = 47.62 μA. The measured value is Peak response current (μA) = 0.2499 x electrical conductivity (mS/m) + 34.932 = 0.2759 x 16.7 + 34.932 = 39.12 μA.

There is a difference of approximately 8.5 μA between the calculated value and the measured value. When this 8.5 μA is converted to dissolved hydrogen concentration, it becomes Dissolved hydrogen concentration difference (ppm) = 0.0077 x 1.5 x Current peak value (μA) = 0.0077 x 1.5 x 8.5 = 0.098 ppm. Whether this difference is within the acceptable range or not seems to depend on the application, and electrical conductivity correction may be necessary depending on the application of the aqueous solution being measured.

As explained in relation to Table 5, when producing hydrogen water from Japanese tap water, if a calibration curve is obtained using standard water with an electrical conductivity of approximately 10 mS/m as a standard for hydrogen concentration and peak value of response current (or peak current density), the effect of electrical conductivity on the measurement results can be ignored when producing hydrogen water from Japanese tap water. In addition to tap water, electrical conductivity can also be ignored when measuring mineral water, blood, infusions, dialysis water, etc.

28, when measuring in a wide range of electrical conductivity from 0 to 150 mS/m, it is desirable to perform a correction. Here, the saturated hydrogen concentration at an electrical conductivity of 16.4 mS/m is 1.6 ppm, and from the relationship between the peak current density value at a current density of 150 μA/cm ² (current value 100 μA) of the peak value of the response current and the dissolved hydrogen concentration, the saturated concentration is: Dissolved hydrogen concentration (ppm) = 0.0077 × current density (μA/cm ² ) + 1.05 = 0.0077 × 150 + 1.05 = 2.20 (ppm). The electrical conductivity at the peak value of 100 μA is calculated by converting the peak value of the response current (μA) = 0.2499 × electrical conductivity (mS/m) + 34.932 to electrical conductivity (mS/m) = (peak value (μA) - 34.932)/0.2499 = (100 - 34.932)/0.2499 = 260 (mS/m). FIG. 33 shows the characteristics of the saturated hydrogen concentration versus electrical conductivity, where the saturated hydrogen concentration is 1.6 ppm when the electrical conductivity is 16.4 mS/m, and the saturated hydrogen concentration is 2.2 ppm when the electrical conductivity is 260 mS/m. In the figure, the horizontal axis is electrical conductivity (mS/m), and the vertical axis is saturated hydrogen concentration (ppm).

From the figure, it can be seen that the formula: calculated saturation hydrogen concentration (ppm) = 0.0025 × electrical conductivity (mS/m) + 1.5596 is true. This result is summarized in Table 10 along with the measured value results. In Table 10, the calculated saturation hydrogen concentration is calculated as calculated saturation hydrogen concentration (ppm) = 0.0025 × electrical conductivity (mS/m) + 1.5596, the peak value of the response current is calculated as peak value of the response current (μA) = 0.2499 × electrical conductivity (mS/m) + 34.932, and the dissolved hydrogen concentration is calculated as dissolved hydrogen concentration (ppm) = 0.0077 × 1.5 × current peak value (μA) + 1.05. In addition, the difference between the calculated saturated hydrogen concentration (ppm) and the measured calculated saturated hydrogen concentration (ppm) is the hydrogen concentration difference (ppm), which is given by hydrogen concentration difference (ppm)=-0.0004×electrical conductivity (mS/m)+0.1061.

Figure 34 shows the relationship between electrical conductivity (mS/m) and hydrogen concentration difference (ppm) in Table 10. In this figure, the horizontal axis is electrical conductivity (mS/m) and the vertical axis is hydrogen concentration difference (ppm). Correction based on electrical conductivity can be performed by adding the hydrogen concentration difference shown in the figure to the dissolved hydrogen concentration calculated from the peak value of the response current.

In other words, the corrected calculated hydrogen concentration can be calculated as follows: Corrected calculated hydrogen concentration (ppm) = 0.0077 x 1.5 x current peak value (μA) + 1.05 - (0.0004 x electrical conductivity (mS/m)) + 0.1061 = 0.0077 x 1.5 x current peak value (μA) - 0.0004 x electrical conductivity (mS/m) + 1.156.

When the corrected calculated hydrogen concentration is calculated using this formula, it is as shown in Table 11.

As can be seen from Table 11, the above correction methods result in almost the same dissolved hydrogen concentration.

Incidentally, when the corrected calculated hydrogen concentration is obtained by multiplication correction instead of additive correction as described above, it is as shown in Table 12. In Table 12, the calculated saturated hydrogen concentration is calculated by calculated saturated hydrogen concentration (ppm) = 0.0025 x electrical conductivity (mS/m) + 1.5596, the peak value of the response current is calculated by peak value of the response current (μA) = 0.2499 x electrical conductivity (mS/m) + 34.932, and the dissolved hydrogen concentration is calculated by dissolved hydrogen concentration (ppm) = 0.0077 x 1.5 x current peak value (μA) + 1.05. The ratio of the calculated saturated hydrogen concentration (ppm) to the measured calculated saturated hydrogen concentration (ppm) is the hydrogen concentration ratio, which is given by hydrogen concentration ratio = calculated saturated hydrogen concentration (ppm) / measured calculated saturated hydrogen concentration (ppm).

Figure 35 shows the relationship between electrical conductivity (mS/m) and hydrogen concentration ratio (saturation/measurement) in Table 12. In this figure, the horizontal axis is electrical conductivity (mS/m) and the vertical axis is hydrogen concentration ratio (saturation/measurement). The hydrogen concentration ratio (saturation/measurement) is a correction coefficient, and correction based on electrical conductivity can be performed by multiplying the dissolved hydrogen concentration calculated from the peak value of the response current by the water hydrogen concentration ratio (saturation/measurement) shown in the figure, i.e., the correction coefficient.

From Figure 35, the relationship of correction coefficient = -0.0003 x electrical conductivity (mS/m) + 1.0708 holds, so the corrected calculated hydrogen concentration can be calculated as follows: Corrected calculated hydrogen concentration (ppm) = (0.0077 x 1.5 x current peak value (μA) + 1.05) x (-0.0003 x electrical conductivity (mS/m) + 1.0708).

When the corrected calculated hydrogen concentration is calculated using this formula, it is as shown in Table 13.

As can be seen from Table 13, this correction method results in an error of about 2%, but the dissolved hydrogen concentration is approximately the same.

In this embodiment, the results of the study on the reproducibility of CV measurements and the measurability of dissolved hydrogen concentration, the results of the study on the correspondence between the peak value of the response current by CV measurement and the dissolved hydrogen concentration by GC measurement, the results of the study on the absence of a polishing pretreatment for CV measurements for the working electrode, the results of the study on the reproducibility and durability of the working electrode, the results of the study on the variation in the peak value of the response current that occurred in the durability test, and the results of the study on the CV measurement of hydrogen water prepared based on tap water as an actual sample were the same as those of the first embodiment.

As described above, according to the dissolved hydrogen concentration measuring device of this embodiment, the peak value of the response current is detected by CV measurement using a Pt-BDD electrode as the working electrode, and the dissolved hydrogen concentration in the measured liquid is obtained, so that the dissolved hydrogen concentration can be measured with good reproducibility by electrochemical measurement. In addition, since a Pt-BDD electrode is used, polishing of the electrode before measurement is not required, and the dissolved hydrogen concentration can be measured stably and with high sensitivity. In addition, the Pt-BDD electrode has been confirmed to have good stability and durability when repeatedly measured. Furthermore, since the peak value of the detected response current is corrected according to the electrical conductivity of the measured liquid, the dissolved hydrogen concentration can be measured correctly and accurately even in a measured liquid in which electrical conductivity must be taken into consideration.

In the second embodiment described above, the peak value of the response current is corrected according to the electrical conductivity value input from the selection switch 116, but it is also possible to provide a sensor that measures the electrical conductivity of the measured liquid 111, and correct the peak value of the response current according to the electrical conductivity value measured by this sensor.

The dissolved hydrogen concentration measuring device of this embodiment is suitable for use when measuring the dissolved hydrogen concentration of a liquid to be measured, in which electrical conductivity must be taken into consideration. In other words, when the liquid to be measured has a wide electrical conductivity range, such as exceeding 100 mS/m, it may be necessary to take electrical conductivity into consideration. This is the case, for example, when pure water, drinking water, carbonated water, soy sauce, dressing, juice, and other liquids to be measured are measured using the same measuring device.

In the embodiment described above, the CV measurement circuit linearly sweeps the potential difference between the working electrode and the reference electrode to detect the peak value of the response current flowing between the working electrode and the counter electrode, but if the potential difference at which the peak value appears can be predicted, that potential difference or a potential difference within a predetermined range including that potential difference may be applied between the working electrode and the reference electrode to measure the peak response current and calculate the dissolved hydrogen concentration. This simplifies the circuit configuration and makes it possible to provide a small, inexpensive dissolved hydrogen concentration measurement device.

The above-described embodiments are illustrative of the present invention and are not limiting, and the present invention can be implemented in various other modified and altered forms. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

10, 110 Cell 11, 111 Test solution 12, 112 Working electrode (WE)
12a, 112a Silicon substrate 12b, 112b BDD film 12c, 112c Pt
13, 113 Reference electrode (RE)
14, 114 Counter electrode (CE)
15, 115 Measuring circuit 15a, 115a Potentiostat 15b, 115b Information processing device 116 Selection switch

Claims (17)

a working electrode immersed in a liquid to be measured, and a measurement circuit for applying a predetermined potential to the working electrode and measuring a response current to obtain a dissolved hydrogen concentration in the liquid to be measured,
13. A dissolved hydrogen concentration measuring device, wherein the working electrode is an electrode in which conductive diamond is modified with platinum. The dissolved hydrogen concentration measuring device according to claim 1, characterized in that the conductive diamond is a boron-doped polycrystalline diamond thin film, and the platinum is platinum electrodeposited on the surface of the polycrystalline diamond thin film. The dissolved hydrogen concentration measuring device according to claim 1 or 2, characterized in that it comprises a working electrode that transfers electrons, a reference electrode that serves as a potential reference for the working electrode, and a counter electrode that forms a current circuit with the working electrode, and the measurement circuit is configured to linearly sweep the potential difference between the working electrode and the reference electrode to measure the response current that flows between the working electrode and the counter electrode. The dissolved hydrogen concentration measuring device according to claim 1 or 2, characterized in that the measurement circuit is configured to apply a potential difference between the working electrode and the reference electrode that is assumed to be the potential difference at which a peak value appears in the response current flowing between the working electrode and the counter electrode, or a potential difference within a predetermined range including the potential difference, to measure the response current. The dissolved hydrogen concentration measuring device according to claim 3 or 4, characterized in that the measurement circuit is configured to obtain the dissolved hydrogen concentration in the measured liquid from the peak value of the measured response current. The dissolved hydrogen concentration measuring device according to claim 5, characterized in that the measuring circuit includes a peak value detecting means for detecting a peak value of the measured response current, and a dissolved hydrogen concentration extracting means for obtaining the dissolved hydrogen concentration using a preset relationship between the peak value detected by the peak value detecting means and the dissolved hydrogen concentration. The dissolved hydrogen concentration measuring device according to any one of claims 3 to 6, characterized in that the measurement circuit is configured to correct the obtained dissolved hydrogen concentration in the measured liquid according to the electrical conductivity of the measured liquid. The dissolved hydrogen concentration measuring device according to claim 7, characterized in that the measurement circuit is configured to correct the obtained dissolved hydrogen concentration by adding a hydrogen concentration difference to the obtained dissolved hydrogen concentration or by multiplying the obtained dissolved hydrogen concentration by a hydrogen concentration ratio. An electrode for a dissolved hydrogen concentration measuring device, which is used as a working electrode of the dissolved hydrogen concentration measuring device described in any one of claims 1 to 8, and is characterized in that the surface of a conductive diamond is modified with platinum. A method for measuring dissolved hydrogen concentration, comprising the steps of: immersing a working electrode, which is an electrode having a conductive diamond surface modified with platinum, in the liquid to be measured; applying a predetermined potential to the working electrode; and measuring the response current, thereby obtaining the dissolved hydrogen concentration in the liquid to be measured. The method for measuring dissolved hydrogen concentration according to claim 10, characterized in that the working electrode is an electrode in which platinum is electrodeposited on the surface of a boron-doped polycrystalline diamond thin film. The method for measuring the concentration of dissolved hydrogen according to claim 9 or 10, characterized in that the concentration of dissolved hydrogen in the liquid to be measured is obtained by linearly sweeping the potential difference between the working electrode, which receives and transfers electrons, and a reference electrode, which serves as a potential reference for the working electrode, and measuring the response current flowing between the working electrode and the counter electrode. The method for measuring a dissolved hydrogen concentration according to claim 9 or 10, characterized in that a potential difference that is assumed to be the potential difference at which a peak value appears in the response current flowing between the working electrode and the counter electrode, or a potential difference in a predetermined range including the potential difference, is applied between the working electrode and the reference electrode to measure the response current. The method for measuring the concentration of dissolved hydrogen according to claim 12 or 13, characterized in that the concentration of dissolved hydrogen in the liquid to be measured is obtained from the peak value of the measured response current. The method for measuring the dissolved hydrogen concentration according to claim 14, characterized in that the peak value of the measured response current is detected, and the dissolved hydrogen concentration is calculated using a preset relationship between the detected peak value and the dissolved hydrogen concentration. The method for measuring the concentration of dissolved hydrogen according to any one of claims 12 to 15, characterized in that the obtained dissolved hydrogen concentration in the liquid to be measured is corrected according to the electrical conductivity of the liquid to be measured. The method for measuring dissolved hydrogen concentration according to claim 16, characterized in that the obtained dissolved hydrogen concentration is corrected by adding a hydrogen concentration difference to the obtained dissolved hydrogen concentration or by multiplying the obtained dissolved hydrogen concentration by a hydrogen concentration ratio.