Hydrogen supply system and reference electrode system

Abstract

The present invention provides a hydrogen supply system that can supply hydrogen to a reversible hydrogen electrode constituting the reference electrode of an electrochemical measuring instrument over a long period of time, and that can be used even in environments where high-pressure gas cylinders cannot be used, and a reference electrode system equipped with this hydrogen supply system. [Solution] The hydrogen supply system comprises a solid polymer water electrolyzer 1 that generates hydrogen gas by electrolyzing water, a gas-liquid separator 2 into which the hydrogen gas generated by the solid polymer water electrolyzer 1 is introduced and which removes water contained in the hydrogen gas, and a hydrogen supply line 3 for supplying the hydrogen gas from which water has been removed by the gas-liquid separator 2 to a reversible hydrogen electrode. The reference electrode system comprises the above hydrogen supply system A and a reversible hydrogen electrode B to which hydrogen gas is supplied from the hydrogen supply system A, and preferably further comprises a liquid level holding mechanism 8 and a hydrogen concentration management mechanism 9 that can maintain a constant liquid level and hydrogen concentration in the reversible water electrode B.

Description

Technical Field

[0001] The present invention relates to a hydrogen supply system capable of supplying hydrogen to a reversible hydrogen electrode constituting a reference electrode of an electrochemical measurement device over a long period of time, and a reference electrode system for an electrochemical measurement device including this hydrogen supply system.

Background Art

[0002] Conventionally, an electrochemical measurement method has been used to evaluate the corrosion resistance of metal materials. In particular, in recent years, research on fuel cells and water electrolysis devices has been promoted as an effort towards achieving carbon neutrality. Since these devices use various metal materials over a long period of time, electrochemical measurement is widely used for evaluating the corrosion resistance and electrochemical characteristics of the metal materials (for example, Patent Document 1). Members used in commercial water electrolysis devices and fuel cells are required to have durability that satisfies a lifespan of 30,000 to 80,000 hours. Since water electrolysis devices and fuel cells are systems that involve electrochemical reactions inside, in order to evaluate the durability of the members used, evaluation by long-term electrochemical measurement is required.

[0003] When evaluating durability of tens of thousands of hours, it is assumed that accelerated degradation tests such as load fluctuation tests will be used. For example, in the "C-10 (III-3-3) test name: potential cycle (load response) test method" of the "NEDO PEFC cell evaluation analysis protocol", there is an evaluation method of repeating a potential cycle test of 0.95V ⇔ 0.6V (each 3 s) 400,000 times, and in this case, it is a continuous test of about 28 days. This test is originally to be carried out on a PEFC single cell, but from the perspective of member evaluation, it is natural to consider evaluating a single member with a three-electrode type electrochemical measurement cell.

[0004] In electrochemical measurement, a reference electrode is used as an electrode that relatively represents the electrode potential of a metal material in a solution. Considering performing electrochemical measurement in units of one month as described above, the stability of the continuous evaluation of the reference electrode to be used becomes very important. The electrode potential of metal materials in fuel cells and water electrolysis cells changes in response to changes in internal pH. Therefore, when used for electrochemical measurements, the potential is generally expressed relative to a reversible hydrogen electrode (hereinafter referred to as "RHE"). For this reason, the RHE is used as the reference electrode during electrochemical measurement tests. Since RHE is a reference electrode that defines the potential by utilizing the oxidation-reduction reaction of hydrogen on an electrode with a platinum-blackened platinum surface, the electrode and electrolyte must be saturated with hydrogen. Therefore, hydrogen gas must be supplied while using RHE.

[0005] While hydrogen gas cylinders and canisters are commonly used as sources of hydrogen gas for RHEs, the following are some of the conventionally known hydrogen gas supply systems for RHEs. (1) A method of supplying hydrogen gas from a high-pressure hydrogen cylinder or experimental hydrogen gas pipe. (2) A method of supplying hydrogen gas from a canister container having a hydrogen storage alloy, or a method of supplying hydrogen gas from a hydrogen storage alloy installed inside the RHE. (3) A method of using platinum wires in the RHE to conduct electric current and perform electrolysis of water, storing the generated hydrogen gas in the RHE, or a method of using hydrogen gas generated in the RHE in real time. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-196737 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, conventional hydrogen supply systems for RHEs have a limited amount of hydrogen that can be stored in the hydrogen source, and hydrogen is depleted during long-term electrochemical measurements. To avoid this, the hydrogen source must be replaced before depletion occurs, but replacing it without interrupting the test is not easy and the test method is cumbersome, making it undesirable. For this reason, it has been virtually impossible to continuously perform electrochemical measurements for 30 days or more under conventional conditions. Furthermore, the method of supplying hydrogen gas from high-pressure hydrogen cylinders cannot be implemented in environments where high-pressure gas cylinders cannot be used. Furthermore, when using hydrogen generated by water electrolysis within the RHE, the solution (internal liquid) within the RHE itself is consumed, leading to depletion of the solution during long-term electrochemical measurements. In addition, the consumption of the solution within the RHE causes changes in the solution's concentration and pH, which alters the potential of the RHE itself, resulting in a decrease in the accuracy of potential measurements.

[0008] Furthermore, our inventors' investigation revealed that even if the hydrogen content problem described above could be resolved, there are still the following challenges in long-term electrochemical measurements. (i) Since relatively dry hydrogen gas is introduced into the RHE, when hydrogen gas is discharged from the RHE, the solution (water) inside the RHE volatilizes and is discharged along with the hydrogen gas. When electrochemical measurements are performed over a long period, the amount of volatilizing solution increases, so the concentration and pH of the solution inside the RHE change, and the accuracy of the potential measurement decreases. (ii) If gases other than hydrogen gas or contaminants enter the RHE for any reason, the potential of the RHE changes, which can lead to a decrease in the accuracy of potential measurements. In particular, when performing electrochemical measurements over a long period, gas components from the electrochemical measurement cell (such as dissolved oxygen) may penetrate into the RHE, causing a decrease in the hydrogen concentration of hydrogen gas in the RHE and potentially fluctuating the potential of the RHE. Traditionally, long-term electrochemical measurements have rarely been performed, and therefore the issues described in (i) and (ii) above have not been recognized. However, it has become clear that, in order to stably perform long-term electrochemical measurements, there are further challenges, such as those described in (i) and (ii), separate from the issue of hydrogen content.

[0009] Therefore, the object of the present invention is to solve the problems of the prior art described above and to provide a hydrogen supply system that can stably supply hydrogen over a long period of time to a reversible hydrogen electrode (RHE) constituting the reference electrode of an electrochemical measuring device, and that can be used even in environments where high-pressure gas cylinders cannot be used, and a reference electrode system equipped with this hydrogen supply system. Another object of the present invention, in addition to the points mentioned above, is to provide a reference electrode system that can properly maintain the liquid level of the solution (internal liquid) in a reversible hydrogen electrode or properly maintain the hydrogen gas concentration in a reversible hydrogen electrode during long-term electrochemical measurements, thereby enabling more accurate long-term electrochemical measurements. [Means for solving the problem]

[0010] The gist of the present invention for solving the above problems is as follows. [1] A hydrogen supply system for supplying hydrogen to a reversible hydrogen electrode that constitutes the reference electrode of an electrochemical measuring device, A solid polymer water electrolysis device (1) that generates hydrogen gas by electrolyzing water, The hydrogen gas generated in the solid polymer water electrolysis apparatus (1) is introduced into a gas-liquid separator (2) that removes water contained in the hydrogen gas, A hydrogen supply system characterized by comprising a hydrogen supply line (3) for supplying hydrogen gas from which water has been removed by the gas-liquid separator (2) to a reversible hydrogen electrode. [2] The hydrogen supply system described in [1] above, further comprising a humidity control mechanism (4) that measures the humidity of the hydrogen gas flowing from the gas-liquid separator (2) to the hydrogen supply line (3) and adjusts the humidity of the hydrogen gas so that the measured humidity is below a standard value.

[0011] [3] In the hydrogen supply system described in [2] above, The humidity control mechanism (4) is A humidity measuring means (40) for measuring the humidity of hydrogen gas flowing through the hydrogen supply line (3), A hydrogen return line (41) is provided for returning hydrogen gas flowing through the hydrogen supply line (3) to the gas-liquid separator (2) from a position downstream of the humidity measurement position by the humidity measuring means (40) in the hydrogen supply line (3), A switching valve (42) that switches the line so that some or all of the hydrogen gas flowing through the hydrogen supply line (3) flows to the hydrogen return line (41), A hydrogen supply system characterized by comprising a control means (43) that controls the switching valve (42) based on the humidity of the hydrogen gas measured by the humidity measuring means (40) to divert some or all of the hydrogen gas flowing through the hydrogen supply line (3) to the hydrogen return line (41) and return it to the gas-liquid separator (2). [4] A hydrogen supply system in any of the above [1] to [3], characterized in that the solid polymer water electrolyzer (1) does not have a heating means and operates at room temperature. [5] A hydrogen supply system comprising any of the hydrogen supply systems described in [1] to [4] above, further comprising a gas concentration management mechanism (5) that measures the hydrogen concentration of the hydrogen gas flowing through the hydrogen supply line (3) and exhausts the hydrogen gas flowing through the hydrogen supply line (3) to the outside of the line if the measured hydrogen concentration is below a standard value.

[0012] [6] In the hydrogen supply system described in [5] above, The aforementioned gas concentration control mechanism (5) is A gas concentration measuring means (50) for measuring the hydrogen concentration of hydrogen gas flowing through the hydrogen supply line (3), At a position on the downstream side of the hydrogen concentration measurement position by the gas concentration measuring means (50) in the hydrogen supply line (3), a gas exhaust part (51) capable of exhausting the hydrogen gas flowing through the hydrogen supply line (3) to the outside of the line by a switching valve, A hydrogen supply system comprising control means (52) for controlling the switching valve of the gas exhaust part (51) based on the hydrogen concentration of the hydrogen gas measured by the gas concentration measuring means (50) to exhaust the hydrogen gas flowing through the hydrogen supply line (3) from the gas exhaust part (51). [7] In the hydrogen supply system according to any one of [1] to [6] above, the hydrogen supply line (6) for sending the hydrogen gas generated by the solid polymer type water electrolyzer (1) to the gas-liquid separator (2) is provided with a cooler (7) for cooling the hydrogen gas flowing through the line.

[0013] [8] A reference electrode system for an electrochemical measurement device, comprising the hydrogen supply system (A) according to any one of [1] to [7] above and a reversible hydrogen electrode (B) to which hydrogen gas is supplied from the hydrogen supply system (A). [9] In the reference electrode system according to [8] above, the reversible hydrogen electrode (B) is provided with a liquid level holding mechanism (8) for measuring the liquid level of the internal liquid in the electrode, supplying water into the electrode so that the measured liquid level satisfies a reference value, and holding the liquid level of the internal liquid.

[10] In the reference electrode system according to [9] above, The liquid level holding mechanism (8) includes a liquid level measuring means (80) for measuring the liquid level of the internal liquid, a water supply means (81) for supplying water into the electrode to hold the liquid level of the internal liquid, and control means (82) for controlling the water supply means (81) to supply water into the electrode based on the liquid level measured by the liquid level measuring means (80).

[0014]

[11] In any of the reference electrode systems of [8] to

[10] above, further, a hydrogen concentration management mechanism (9) is provided which measures the hydrogen concentration of the hydrogen gas inside the reversible hydrogen electrode (B) or the hydrogen gas discharged from the reversible hydrogen electrode (B), and controls the hydrogen gas supply amount from the hydrogen supply system (A) so that the measured hydrogen concentration becomes not less than a reference value. A reference electrode system for an electrochemical measurement device is characterized by this.

[12] In the reference electrode system of

[11] above, the hydrogen concentration management mechanism (9) includes a gas concentration measurement means (90) which measures the hydrogen concentration of the hydrogen gas inside the reversible hydrogen electrode (B) or the hydrogen gas discharged from the reversible hydrogen electrode (B), and a control means (91) which controls the solid polymer type water electrolysis device (1) based on the hydrogen concentration measured by the gas concentration measurement means (90) to increase or decrease the hydrogen gas generation amount. A reference electrode system for an electrochemical measurement device is characterized by this.

[0015]

[13] An electrochemical measurement device characterized by including any of the hydrogen supply systems (A) of [1] to [7] above and a reversible hydrogen electrode (B) to which hydrogen gas is supplied from the hydrogen supply system (A).

[14] In the electrochemical measurement device of

[13] above, the reversible hydrogen electrode (B) includes a liquid level holding mechanism (8) which measures the liquid level of the internal liquid inside the electrode, and supplies water into the electrode so that the measured liquid level satisfies a reference value, thereby holding the liquid level of the internal liquid. An electrochemical measurement device is characterized by this.

[15] In the electrochemical measurement device of

[14] above, the liquid level holding mechanism (8) includes a liquid level measurement means (80) which measures the liquid level of the internal liquid, a water supply means (81) which supplies water into the electrode to hold the liquid level of the internal liquid, and a control means (82) which controls the water supply means (81) to supply water into the electrode based on the liquid level measured by the liquid level measurement means (80). An electrochemical measurement device is characterized by this.

[0016]

[16] An electrochemical measuring device comprising any of the above

[13] to

[15] , further comprising a hydrogen concentration management mechanism (9) that measures the hydrogen concentration of hydrogen gas inside the reversible hydrogen electrode (B) or hydrogen gas discharged from the reversible hydrogen electrode (B), and controls the amount of hydrogen gas supplied from the hydrogen supply system (A) so that the measured hydrogen concentration is equal to or greater than a standard value.

[17] In the electrochemical measuring apparatus described in

[16] above, The hydrogen concentration control mechanism (9) is A gas concentration measuring means (90) for measuring the hydrogen concentration of hydrogen gas inside the reversible hydrogen electrode (B) or hydrogen gas discharged from the reversible hydrogen electrode (B), An electrochemical measuring device characterized by comprising a control means (91) that controls the solid polymer water electrolysis device (1) to increase or decrease the amount of hydrogen gas generated based on the hydrogen concentration measured by the gas concentration measuring means (90). [Effects of the Invention]

[0017] The hydrogen supply system of the present invention, and the reference electrode system equipped with this hydrogen supply system, can stably supply hydrogen over a long period of time to the reversible hydrogen electrode (RHE) that constitutes the reference electrode of an electrochemical measuring instrument. Therefore, it becomes possible to perform long-term electrochemical measurements, which were previously virtually impossible. Furthermore, it can be used in environments where high-pressure gas cylinders cannot be used. Furthermore, the reference electrode system of the present invention, which is equipped with a liquid level holding mechanism for the internal liquid of the reversible hydrogen electrode, can, in addition to the points mentioned above, properly maintain the liquid level of the internal liquid of the reversible hydrogen electrode during long-term electrochemical measurements, thereby enabling more accurate long-term electrochemical measurements. Furthermore, the reference electrode system of the present invention, which is equipped with a hydrogen concentration control mechanism for managing the hydrogen concentration inside the reversible hydrogen electrode, can, in addition to the points mentioned above, maintain an appropriate hydrogen gas concentration inside the reversible hydrogen electrode during long-term electrochemical measurements, and can perform long-term electrochemical measurements with higher accuracy. [Brief explanation of the drawing]

[0018] [Figure 1] A schematic diagram illustrating one embodiment of the hydrogen supply system of the present invention. [Figure 2] This diagram schematically illustrates the water electrolysis cell of the polymer electrolyte water electrolysis apparatus that constitutes the hydrogen supply system shown in Figure 1. [Figure 3] Figure 1 is a schematic explanatory diagram showing one embodiment of the reference electrode system of the present invention equipped with the hydrogen supply system. [Figure 4] Front view showing the reversible hydrogen electrodes that constitute the reference electrode system in Figure 3. [Figure 5] This diagram schematically illustrates the reversible hydrogen electrode and the liquid level maintenance mechanism that maintains the liquid level of the internal solution, which constitute the reference electrode system shown in Figure 3. [Figure 6] This is a schematic diagram illustrating an electrochemical measurement cell and a reference electrode immersed in the cell, in one embodiment of the electrochemical measuring device of the present invention. [Figure 7] Graph showing the change in the measured potential over time in the electrochemical measurement of the example. [Figure 8] Diagram illustrating a reversible hydrogen electrode having a hydrogen storage alloy cartridge used in Comparative Example 1 of the Examples. [Modes for carrying out the invention]

[0019] ≪Hydrogen Supply System≫ First, the hydrogen supply system of the present invention will be described. Figure 1 schematically shows one embodiment of the hydrogen supply system of the present invention (explanatory diagram). This hydrogen supply system is for supplying hydrogen to a reversible hydrogen electrode that constitutes the reference electrode of an electrochemical measuring device, and comprises a solid polymer water electrolysis device 1 that generates hydrogen gas by electrolyzing water, a gas-liquid separator 2 that removes water contained in the hydrogen gas generated by the solid polymer water electrolysis device 1, and a hydrogen supply line 3 (gas piping system) for supplying the hydrogen gas from which water has been removed by the gas-liquid separator 2 to the reversible hydrogen electrode (hereinafter referred to as "RHE").

[0020] The polymer electrolyte water electrolysis apparatus 1 includes, for example, a proton exchange membrane type water electrolysis cell or an anion exchange membrane type water electrolysis cell, and its basic structure and configuration are the same as conventional ones. On the other hand, conventional polymer electrolyte water electrolysis apparatuses heat the electrolysis environment (electrolysis cell and supplied electrolyte) with a heating means to increase the water electrolysis efficiency, and operate at a higher operating temperature of the water electrolysis cell (usually 50°C or higher and less than 80°C). In contrast to this, in the hydrogen supply system of the present invention, it is more important to have a lower temperature for the generated hydrogen gas than to increase the water electrolysis efficiency, so it is desirable that the polymer electrolyte water electrolysis apparatus 1 does not have a heating means and is configured so that the water electrolysis cell operates at room temperature (usually at an operating temperature of 30°C or lower).

[0021] In this invention, the reasons why it is desirable to lower the operating temperature of the water electrolysis cell and lower the temperature of the generated hydrogen gas are as follows: If the amount of water in the hydrogen gas introduced into the RHE is large, water will mix into the RHE and dilute the internal liquid of the RHE. This will reduce the accuracy of potential measurement due to changes in the concentration and pH of the internal liquid. Therefore, it is desirable that the hydrogen gas introduced into the RHE has as low a humidity as possible. In water electrolysis in the solid polymer water electrolysis apparatus 1, the hydrogen gas discharged from the cathode side is humidified due to the influence of the associated water on the anode side, and its relative humidity is approximately 100% RH. Therefore, although the water in the hydrogen gas is removed by the gas-liquid separator 2 before supplying the RHE, if the temperature of the hydrogen gas is high, the amount of saturated water vapor is high, and the gas-liquid separator 2 cannot sufficiently reduce the humidity of the hydrogen gas. For this reason, it is desirable to lower the operating temperature of the water electrolysis cell as much as possible so that the gas-liquid separator 2 can sufficiently reduce the humidity of the hydrogen gas. For the reasons stated above, the solid polymer water electrolysis apparatus 1 of this embodiment does not have a heating means, and the water electrolysis cell is designed to operate at room temperature (usually at an operating temperature of 30°C or lower). In this polymer electrolyte water electrolysis apparatus 1, electrolyte (pure water or aqueous solution to be electrolyzed) is supplied from the supply tank 15 by the liquid transfer pump 16. The supply tank 15 is replenished with electrolyte as needed. The configuration of the solid polymer water electrolysis apparatus 1 will be explained in detail later.

[0022] The gas-liquid separator 2 receives hydrogen gas generated in the solid polymer water electrolysis device 1 through the hydrogen supply line 6 (gas piping system), and the water contained in the hydrogen gas is removed. The gas-liquid separator 2 can be, for example, (i) a type that incorporates a desiccant and dehumidifies by passing hydrogen gas through this desiccant, (iii) a type that dehumidifies by cooling the hydrogen gas inside and condensing the water, or (iii) a type that uses the above dehumidification methods (i) and (ii) in combination, but is not limited to these. Furthermore, as shown by the dashed line in Figure 1, a cooler 7 (heat exchanger) may be installed in the hydrogen supply line 6, and the water content may be condensed by cooling the hydrogen gas in this cooler 7, thereby improving the water removal efficiency in the gas-liquid separator 2.

[0023] The hydrogen gas from which moisture has been removed in the gas-liquid separator 2 is supplied to the RHE side via the hydrogen supply line 3. As mentioned above, it is desirable that the hydrogen gas introduced into the RHE be as humid as possible. Therefore, it is desirable to have a mechanism that monitors the humidity of the hydrogen gas supplied to the RHE side via the hydrogen supply line 3 and adjusts the humidity as needed. For this reason, this embodiment includes a humidity adjustment mechanism 4 that measures the humidity of the hydrogen gas flowing from the gas-liquid separator 2 to the hydrogen supply line 3 and adjusts the humidity of the hydrogen gas so that the measured humidity is below a standard value. The humidity control mechanism 4 of this embodiment consists of a humidity measuring means 40 for measuring the humidity of hydrogen gas flowing from the gas-liquid separator 2 to the hydrogen supply line 3, a hydrogen return line 41 for returning the hydrogen gas flowing through the hydrogen supply line 3 to the gas-liquid separator 2, a switching valve 42 for flowing hydrogen gas through the hydrogen return line 41, and a control means 43 for controlling the switching valve 42.

[0024] The humidity measuring means 40 is a hygrometer that measures the humidity of the hydrogen gas flowing through the hydrogen supply line 3, and the measurement data is sent to the control means 43. The hydrogen return line 41 (gas piping system) is a line that branches off from a position downstream of the humidity measurement position by the humidity measuring means 40 in the hydrogen supply line 3 and leads to the gas-liquid separator 2. Through this hydrogen return line 41, the hydrogen gas flowing through the hydrogen supply line 3 can be returned (circulated) to the gas-liquid separator 2. The switching valve 42 is installed at the branching point of the hydrogen return line 41 to switch the line so that some or all of the hydrogen gas flowing through the hydrogen supply line 3 flows into the hydrogen return line 41, and in this embodiment it is configured as a three-way valve (for example, a three-way solenoid valve).

[0025] This switching valve 42 is controlled by the control means 43 to switch the lines. The type of switching valve 42 (three-way valve) may be one that switches all of the hydrogen gas flowing through the hydrogen supply line 3 to the hydrogen return line 41, or it may be one that selectively switches some or all of the hydrogen gas flowing through the hydrogen supply line 3 to the hydrogen return line 41. In the latter case, for example, a three-way valve that can be adjusted to an intermediate opening can be used. The control means 43 controls the switching valve 42 based on the humidity of the hydrogen gas measured by the humidity measuring means 40 to divert some or all of the hydrogen gas flowing through the hydrogen supply line 3 to the hydrogen return line 41 and return it to the gas-liquid separator 2. Specifically, in the control form, for example, a reference value (upper limit) for the humidity of the hydrogen gas flowing through the hydrogen supply line 3 is set in the control means 43, and when the humidity measurement value of the hydrogen gas input from the humidity measuring means 40 exceeds this reference value, the switching valve 42 is controlled to divert some or all of the hydrogen gas flowing through the hydrogen supply line 3 to the hydrogen return line 41, so that further moisture removal is performed in the gas-liquid separator 2, and the humidity of the hydrogen gas is adjusted so that the humidity measured by the humidity measuring means 40 is below the reference value. After that, when the humidity measurement value of the hydrogen gas input from the humidity measuring means 40 is below the reference value, the switching valve 42 is returned to its original position and the entire amount of hydrogen gas flows through the hydrogen supply line 3.

[0026] Here, if the entire amount of hydrogen gas flowing through hydrogen supply line 3 is diverted to hydrogen return line 41, hydrogen gas will not be supplied to the RHE while hydrogen gas is flowing through hydrogen return line 41. However, the RHE can operate sufficiently with the residual hydrogen atmosphere in hydrogen supply line 3 downstream of the switching valve 42. Furthermore, within the expected range of operation of this system, the hydrogen gas in hydrogen supply line 3 downstream of the switching valve 42 will not be completely consumed within the RHE during the few seconds it takes for the hydrogen gas returned to hydrogen return line 41 to circulate. Therefore, there are no particular operational problems even if the entire amount of hydrogen gas is returned to hydrogen return line 41. Furthermore, the humidity control mechanism 4 is not limited to this embodiment, as it only needs to be able to measure the humidity of the hydrogen gas flowing from the gas-liquid separator 2 to the hydrogen supply line 3 and adjust the humidity of the hydrogen gas so that the measured humidity is below a standard value. For example, various embodiments are possible, such as providing a dehumidifying bypass line in the middle of the hydrogen supply line 3, and when the humidity of the hydrogen gas exceeds a standard value, controlling a switching valve to divert some or all of the hydrogen gas flowing through the hydrogen supply line 3 to the bypass line, where it is dehumidified by a dehumidifier installed in the bypass line before being returned to the hydrogen supply line 3.

[0027] Furthermore, immediately after the system is started (immediately after electrolysis begins), air is mixed into the hydrogen supply line 3. If the hydrogen gas generated in the water electrolysis cell is directly supplied to the RHE side, air will be supplied to the RHE, potentially causing gas contamination. Therefore, it is desirable to prevent the hydrogen gas flowing through the hydrogen supply line 3 from being supplied to the RHE side while its hydrogen concentration is low. For this reason, this embodiment includes a gas concentration management mechanism 5 that measures the hydrogen concentration of the hydrogen gas flowing through the hydrogen supply line 3 and exhausts the hydrogen gas flowing through the hydrogen supply line 3 to the outside of the line if the measured hydrogen concentration falls below a standard value. The gas concentration management mechanism 5 of this embodiment consists of a gas concentration measuring means 50 for measuring the hydrogen concentration of hydrogen gas flowing through the hydrogen supply line 3, a gas exhaust unit 51 capable of selectively exhausting the hydrogen gas flowing through the hydrogen supply line 3 to the outside of the line, and a control means 52 for controlling the exhaust of gas from the gas exhaust unit 51.

[0028] The gas concentration measuring means 50 is a hydrogen concentration meter that measures the hydrogen concentration of hydrogen gas flowing through the hydrogen supply line 3, and the measurement data is sent to the control means 52. The gas exhaust section 51 is located downstream of the hydrogen concentration measurement position by the gas concentration measuring means 50 in the hydrogen supply line 3, and selectively exhausts the hydrogen gas flowing through the hydrogen supply line 3 to the outside of the line using a switching valve. In this embodiment, a three-way valve (for example, a three-way solenoid valve) is used for the switching valve. The control means 52 controls the switching valve of the gas exhaust unit 51 based on the hydrogen concentration of the hydrogen gas measured by the gas concentration measuring means 50, thereby exhausting the hydrogen gas flowing through the hydrogen supply line 3 from the gas exhaust unit 51. Specifically, as an example of the control form, the control means 52 sets a reference value (lower limit) for the hydrogen concentration of the hydrogen gas flowing through the hydrogen supply line 3, and when the hydrogen concentration measurement value of the hydrogen gas input from the gas concentration measuring means 50 falls below this reference value, it controls the switching valve of the gas exhaust unit 51 to exhaust the hydrogen gas flowing through the hydrogen supply line 3 to the outside of the line, preventing it from being supplied to the RHE side. Subsequently, when the hydrogen concentration measurement value of the hydrogen gas input from the gas concentration measuring means 50 becomes equal to or greater than the reference value, the switching valve of the gas exhaust unit 51 is returned to its original position to stop the exhaust of hydrogen gas and supply hydrogen gas to the RHE side.

[0029] It should be noted that the gas concentration management mechanism 5 is not limited to this embodiment, as it only needs to be able to measure the hydrogen concentration of the hydrogen gas flowing through the hydrogen supply line 3 and exhaust the hydrogen gas flowing through the hydrogen supply line 3 to the outside of the line if the measured hydrogen concentration is below a standard value. For example, a bypass line branching off from the hydrogen supply line 3 may be provided, and a switching valve may be used to allow hydrogen gas to flow through this bypass line. If the measured hydrogen concentration is below a standard value, the mechanism may be used to exhaust the hydrogen gas flowing through the hydrogen supply line 3 into the bypass line. In this case, a gas separator that allows only hydrogen gas to pass through may be provided in the bypass line to supply only hydrogen gas to the RHE side, or the gas may be exhausted directly into the atmosphere from the bypass line. The gas concentration management mechanism 5 can take various forms, including the above embodiment. The control means 43 constituting the humidity control mechanism 4 described above, and the control means 52 constituting the gas concentration management mechanism 5, are implemented as functions of a microcomputer.

[0030] The hydrogen supply line 3 may be equipped with a mass flow meter and a pressure regulating valve to adjust the hydrogen gas flow rate, if necessary. However, the hydrogen gas flow rate can basically be adjusted by controlling the current during water electrolysis. Furthermore, if there is a risk of the purity of hydrogen gas decreasing due to a crossover phenomenon in which oxygen gas generated on the oxygen electrode side of the solid polymer water electrolysis apparatus 1 permeates to the hydrogen electrode side, an oxygen gas / hydrogen gas separator may be installed in the hydrogen supply line 3. If the purity of the hydrogen gas is not sufficiently high, the accuracy of the RHE potential measurement may decrease. As for this oxygen / hydrogen gas separator, for example, one that separates oxygen gas and hydrogen gas using a gas separation membrane, one equipped with a metal material that preferentially permeates only hydrogen gas, or one that separates oxygen gas and hydrogen gas using an oxygen scavenger can be used.

[0031] Next, we will explain the details of the configuration of the solid polymer water electrolysis apparatus 1. Figure 2 is a schematic diagram (explanatory diagram) of the water electrolysis cell of the solid polymer water electrolysis apparatus 1. This water electrolysis cell has as its basic structure a membrane-electrode assembly (MEA) composed of a proton exchange type or anion exchange type solid polymer membrane 10, catalyst layers 11 (oxygen evolution electrode catalyst and hydrogen evolution electrode catalyst) on both sides thereof, and diffusion layers 12 on both sides thereof. A single water electrolysis cell is formed by sandwiching this MEA from both sides with separators 13 and fastening them together. The solid polymer membrane 10 typically uses a proton exchange membrane or an anion exchange membrane. In this invention, the gas purity of hydrogen gas is more important than the water electrolysis efficiency, so in order to suppress the decrease in gas purity due to the gas crossover phenomenon, it is preferable to use a thick-film type with a larger film thickness than that of a solid polymer membrane that is normally used. Specifically, for the proton exchange membrane type, it is preferable to use one with a film thickness of about 180 to 200 μm, and a specific example is N117 (manufactured by DuPont), which is a representative Nafion membrane. For the anion exchange membrane type, it is preferable to use one with a film thickness of about 70 to 150 μm, and a specific example is FAB-PK-130 (manufactured by Fumasep). The crossover phenomenon is a phenomenon in which gases generated at each electrode (in this case, oxygen gas or hydrogen gas) permeate through a solid polymer membrane and mix with the gases at the opposite electrode. When this phenomenon becomes pronounced, not only does the hydrogen concentration of the generated hydrogen gas decrease, but there is also a risk of the gas composition becoming explosive, which is dangerous.

[0032] Materials such as platinum-supported carbon or platinum black nanoparticles are commonly used for the catalyst layer 11 (electrode catalyst) on the hydrogen electrode side (hydrogen generation side). The catalyst layer 11 is fixed to the solid polymer film 10 by thermal compression bonding these materials together with a slurry containing the same components as the solid polymer film 10. Carbon paper or carbon cloth is commonly used for the diffusion layer 12 on the hydrogen electrode side (hydrogen generation side). Carbon materials or metal materials coated with precious metals (generally titanium or stainless steel) are commonly used for the separator 13 on the hydrogen electrode side. In the case of an anion exchange membrane type water electrolysis cell, it is preferable to use precious metal coated stainless steel, more preferably pure Ni or a Ni alloy, for the separator 13 on the hydrogen electrode side.

[0033] The water electrolysis cell operates when a direct current is passed through the catalyst layer 11 (electrode catalyst) that makes up the water electrolysis cell. A liquid supply line 17 (supply pipe) from a supply tank 15 is connected to the anode side (oxygen electrode side) of the water electrolysis cell, and the electrolyte (pure water or aqueous solution for water electrolysis, etc.) in the supply tank 15 is supplied to the water electrolysis cell by a liquid supply pump 16. The electrolyte is supplied only to the anode side of the water electrolysis cell. As the liquid transfer pump 16, it is preferable to use a pump whose wetted parts are made of a material that does not corrode. In particular, in an anion exchange membrane type water electrolysis cell, potassium hydroxide solution (KOH) is used as the electrolyte, so there is a risk that the metal of the wetted parts of the pump may corrode due to the alkali. For this reason, it is preferable to use a plunger pump or diaphragm pump whose wetted parts are made of PTFE, for example. Alternatively, a chemical-resistant tube pump may be used. Furthermore, a return line 18 is provided to return the electrolyte that was not electrolyzed in the water electrolysis cell, along with the oxygen gas generated on the anode side (oxygen electrode side), back to the supply tank 15.

[0034] Next, the usage configuration of the hydrogen supply system of this embodiment will be described. The system is started by applying a direct current to the electrodes of the water electrolysis cells that make up the solid polymer water electrolysis apparatus 1, and by supplying electrolyte (pure water or aqueous solution to be electrolyzed) from the supply tank 15 through the supply line 17 using the liquid supply pump 16. In the case of proton exchange membrane type water electrolysis, the electrolyte supplied to the water electrolysis cell is pure water, preferably ion-exchanged water with an conductivity of 1 μS / cm or less, and more preferably ultrapure water with an conductivity of 0.06 μS / cm or less. In the case of anion exchange membrane type water electrolysis, the electrolyte supplied to the water electrolysis cell is generally a potassium hydroxide solution (KOH) with a concentration of about 0.1 M to 1 M.

[0035] The amount of electrolyte supplied to a water electrolysis cell is typically 1 cm² over an electrode area. 2 A good guideline is to aim for a flow rate of approximately 2 mL / min to 10 mL / min per unit area. The DC current supplied to the water electrolysis cell depends on the internal liquid volume of the RHE, but it is appropriate to set the current value such that the hydrogen generation rate is between 0.1 mL / min and less than 1 mL / min for every 1 mL of internal liquid volume of the RHE. The hydrogen gas generated in the solid polymer water electrolysis apparatus 1 is introduced to the gas-liquid separator 2 via the hydrogen supply line 6, where water is removed, and then supplied to the RHE side via the hydrogen supply line 3. If the hydrogen supply line 6 is equipped with a cooler 7, the hydrogen gas is cooled by the cooler 7 before being introduced to the gas-liquid separator 2. The electrolyte that was not electrolyzed in the water electrolysis cell is returned to the supply tank 15 via the return line 18 along with the oxygen gas generated on the anode side (oxygen electrode side), and is supplied back to the water electrolysis cell. The oxygen gas introduced into the supply tank 15 is then released.

[0036] Immediately after the system starts up (immediately after electrolysis begins), air is mixed into the hydrogen supply line 3. If the hydrogen gas generated in the water electrolysis cell is directly supplied to the RHE side, air will be supplied to the RHE, potentially causing gas contamination. Therefore, it is desirable to prevent the supply of hydrogen gas to the RHE side until the hydrogen concentration of the hydrogen gas flowing through the hydrogen supply line 3 becomes sufficiently high after the system starts up. For this reason, the gas concentration management mechanism 5 measures the hydrogen concentration of the hydrogen gas flowing through the hydrogen supply line 3, and if the measured hydrogen concentration is below the standard value, it exhausts the hydrogen gas flowing through the hydrogen supply line 3 to the outside of the line. In other words, the hydrogen concentration of the hydrogen gas flowing through the hydrogen supply line 3 is measured continuously or at regular time intervals by the gas concentration measuring means 50, and the measured value is sent to the control means 52. The control means 52 is configured to have, for example, a reference value for the hydrogen concentration of the hydrogen gas (for example, a lower limit of 99 vol%). When the hydrogen concentration measurement input from the gas concentration measuring means 50 falls below this reference value, the control means 52 controls the switching valve of the gas exhaust section 51 to open the gas exhaust section 51 (open the exhaust side of the three-way valve), and exhausts the hydrogen gas flowing through the hydrogen supply line 3 to the outside of the line. Then, when the hydrogen concentration measurement input from the gas concentration measuring means 50 meets the reference value, the control means 52 controls the switching valve of the gas exhaust section 51 to close the gas exhaust section 51 (close the exhaust side of the three-way valve), allowing the hydrogen gas to flow through the hydrogen supply line 3 to the RHE side.

[0037] After moisture is removed from the hydrogen gas in the gas-liquid separator 2, it is supplied to the RHE side via the hydrogen supply line 3. Since it is desirable for the hydrogen gas introduced into the RHE to have as low a humidity as possible, the humidity control mechanism 4 measures the humidity of the hydrogen gas flowing through the hydrogen supply line 3 and adjusts the humidity of the hydrogen gas so that the measured humidity is below a standard value. That is, the humidity of the hydrogen gas flowing through the hydrogen supply line 3 is measured continuously or at regular time intervals by the humidity measuring means 40, and the measured values ​​are sent to the control means 43. The control means 43 is configured, for example, to have a standard value for the humidity of the hydrogen gas (for example, an upper limit of 1%RH). When the humidity measurement value input from the humidity measuring means 40 exceeds this standard value, the switching valve 42 is controlled to open (open the hydrogen return line 41 side of the three-way valve) or partially open the hydrogen return line 41 side and close (close the hydrogen supply line 3 side of the three-way valve) or partially close the hydrogen supply line 3 side, thereby directing some or all of the hydrogen gas flowing through the hydrogen supply line 3 to the hydrogen return line 41 and returning it to the gas-liquid separator 2. The hydrogen gas returned to the gas-liquid separator 2 undergoes further dehumidification before flowing back into the hydrogen supply line 3. Then, when the humidity measurement value input from the humidity measuring means 40 meets the reference value, the control means 43 controls the switching valve 42 to close the hydrogen return line 41 side (close the hydrogen return line 41 side of the three-way valve) and open the hydrogen supply line 3 side (open the hydrogen supply line 3 side of the three-way valve), and supplies the hydrogen gas from which moisture has been removed in the gas-liquid separator 2 directly to the RHE side through the hydrogen supply line 3. Furthermore, if the hydrogen supply line 3 is equipped with an oxygen / hydrogen gas separator, the hydrogen gas flowing through the hydrogen supply line 3 will have its oxygen removed in this separator, and after its purity is, for example, 99 vol% or higher, it will be supplied to the RHE side.

[0038] ≪Reference Electrode System≫ Next, the reference electrode system of the present invention, which includes the hydrogen supply system described above (hereinafter referred to as "hydrogen supply system A"), will be described. The reference electrode system of the present invention comprises a hydrogen supply system A as described above, and a reversible hydrogen electrode B (hereinafter referred to as "RHE[B]") to which hydrogen gas is supplied from this hydrogen supply system. Figure 3 schematically shows one embodiment of the reference electrode system of the present invention equipped with the hydrogen supply system of Figure 1 (explanatory diagram). Here, the hydrogen supply system A is the same as described in the embodiment of Figure 1, so the same reference numerals are used and a detailed explanation is omitted.

[0039] Figure 4 shows the RHE[B] used as a reference electrode in the embodiment of Figure 3 (front view). The RHE[B] is a single-junction type and consists of a glass support tube 20 (RHE housing), a platinum electrode 21 (platinum-blackened electrode) placed inside the tip of the support tube 20, a platinum wire 22 connected to the platinum electrode 21, a hydrogen gas inlet tube 23 arranged along the inside of the support tube 20 and supplying hydrogen gas from the tip to the platinum electrode 21, a ceramic porous body 24 that constitutes the liquid junction at the tip of the support tube 20, and an internal liquid 25 filled inside the support tube 20. This internal liquid is usually an electrolyte with the same pH as the test solution. Other components in Figure 4 include 230, the gas outlet at the tip of the hydrogen gas inlet tube 23, 231, the gas inlet for supplying hydrogen gas to the hydrogen gas inlet tube 23, and 26, the gas outlet for discharging hydrogen gas from inside the support tube 20. The configuration of the reference electrode (RHE) described above is the same as that of a known RHE in conventional use.

[0040] Since the base material of the support tube 20 is made of transparent glass, the platinum electrode 21, platinum wire 22, hydrogen gas introduction tube 23, ceramic porous body 24, etc., which are arranged inside the support tube 20 are represented by solid lines in Figure 4. The end of the hydrogen supply line 3 of the hydrogen supply system A is connected to the gas inlet 231 of the hydrogen gas introduction pipe 23, and hydrogen gas is introduced into RHE[B] through this hydrogen supply line 3. A gas exhaust line 14 is connected to the gas outlet 26 of RHE[B], and hydrogen gas introduced into RHE[B] from the hydrogen supply line 3 passes through RHE[B] before being led from the gas outlet 26 to the gas exhaust line 14. A water seal pipe or check valve is provided at the end of the gas exhaust line 14 to prevent air from entering, and the hydrogen gas is released through this water seal pipe or check valve.

[0041] As mentioned earlier, low-humidity hydrogen gas is introduced into the RHE[B], so when hydrogen gas is discharged from the RHE, the internal liquid (water) of the RHE volatilizes and is discharged along with the hydrogen gas. When electrochemical measurements are performed over a long period, the amount of internal liquid (water) that volatilizes increases, so the concentration and pH of the internal liquid of the RHE changes, and the accuracy of the potential measurement decreases. The amount of internal liquid (water) that volatilizes from the RHE[B] varies depending on the balance between the hydrogen gas flow rate and the volume of internal liquid of the RHE, the installation environment (temperature, humidity), the test temperature (temperature of the internal liquid of the RHE), the structure of the RHE, etc., so it cannot be stated in general terms, but for example, in the case of an acidic solution (pH 1), when the internal liquid (water) volatilizes and the liquid level (volume) becomes 1 / 10 of the initial level, the internal liquid (electrolyte) is concentrated 10 times, and the pH decreases by 1. Then, when the pH decreases by 1 in this way, theoretically the potential of the RHE itself will increase by 59.1 mV. Therefore, in order to perform stable potential measurements over a long period of time, it is desirable to have a mechanism that monitors the liquid level of the internal solution in the RHE[B] and maintains the liquid level by supplying water as needed. For this reason, the RHE[B] of this embodiment is equipped with a liquid level maintenance mechanism 8 that measures the liquid level of the internal solution in the electrode and supplies water into the electrode so that the measured liquid level meets a reference value, thereby maintaining the liquid level of the internal solution.

[0042] Figure 5 schematically shows the RHE[B] and liquid level holding mechanism 8 that constitute the reference electrode system of Figure 3 (explanatory diagram). The liquid level holding mechanism 8 of this embodiment consists of a liquid level measuring means 80 for measuring the liquid level of the internal liquid, a water supply means 81 for supplying water into the electrode to maintain the liquid level of the internal liquid, and a control means 82 for controlling the water supply means 81. The liquid level measuring means 80 is a level sensor that detects the liquid level position. It can be a contact type (e.g., float type) or a non-contact type (e.g., capacitive, ultrasonic, radar type), but in this embodiment, a non-contact capacitive level sensor (a type that is attached to the support tube 20) is used. This capacitive level sensor is one of the general level sensors and detects the liquid level position by measuring the capacitance generated between a pair of electrodes and correlating this change with a change in liquid level.

[0043] The water supply means 81 includes a water supply tank 810 provided on the outside of the support pipe 20 of the RHE[B], a water supply pipe 811 extending from the water supply tank 810 into the support pipe 20, and an on / off valve 812 (solenoid valve) provided in the water supply pipe 811. The control means 82 controls the water supply means 81 to supply water into the electrode based on the liquid level of the waste liquid measured by the liquid level measuring means 80. Specifically, in the control means 82, a reference range (lower limit and upper limit) for the liquid level of the internal liquid is set, and when the liquid level measurement input from the liquid level measuring means 80 reaches the lower limit of this reference range, the on-off valve 812 of the water supply pipe 811 is opened to supply water from the water supply tank 810, raising the liquid level of the internal liquid and maintaining the liquid level. Subsequently, when the liquid level measurement input from the liquid level measuring means 80 reaches the upper limit of the reference range, the on-off valve 812 is closed to stop the water supply. Furthermore, the liquid level holding mechanism 8 is not limited to this embodiment, as it only needs to be able to measure the liquid level of the internal liquid in the electrode, supply water to the electrode so that the measured liquid level meets a reference value, and maintain the liquid level of the internal liquid. For example, various embodiments can be implemented, such as a mechanism that maintains the liquid level by turning the water supply pump ON / OFF based on signals from various level sensors as described above.

[0044] Furthermore, if gases other than hydrogen gas or contaminants are introduced into RHE[B] due to some factor, the potential of RHE[B] changes, which can lead to a decrease in the accuracy of potential measurement. For example, the internal liquid of RHE[B] is connected to the electrochemical measurement cell via a ceramic porous body 24. Although RHE[B] is basically hydrogen-saturated, if the atmosphere inside the electrochemical measurement cell is, for example, an atmospheric atmosphere, prolonged potential measurement may cause dissolved oxygen in the electrochemical measurement cell to gradually permeate into RHE, reducing the hydrogen concentration of hydrogen gas in RHE and potentially causing fluctuations in the potential of RHE. Therefore, in order to perform stable potential measurement over a long period, it is necessary to always maintain an appropriate hydrogen gas concentration inside RHE[B], and for this purpose, it is desirable to monitor the hydrogen gas concentration inside RHE[B] and manage the gas concentration. For this reason, this embodiment is equipped with a hydrogen concentration management mechanism 9 that measures the hydrogen concentration of hydrogen gas inside RHE[B] or hydrogen gas discharged from RHE[B] and controls the amount of hydrogen gas supplied from the hydrogen supply system A so that the measured hydrogen concentration is equal to or greater than a standard value.

[0045] The hydrogen concentration management mechanism 9 of this embodiment consists of a gas concentration measuring means 90 for measuring the hydrogen concentration of hydrogen gas discharged from RHE[B], and a control means 91 for controlling the solid polymer water electrolysis device 1 to increase or decrease the amount of hydrogen gas generated based on the hydrogen concentration measured by the gas concentration measuring means 90. The gas concentration measuring means 90 is a hydrogen concentration meter that measures the hydrogen concentration of hydrogen gas discharged from RHE[B] into the gas exhaust line 14, and the measurement data is sent to the control means 91. Since the hydrogen concentration of the hydrogen gas discharged into the gas exhaust line 14 is substantially the same as the hydrogen concentration of the hydrogen gas inside RHE[B], the gas concentration measuring means 90 in this embodiment measures the hydrogen concentration of the hydrogen gas discharged into the gas exhaust line 14, but the gas concentration measuring means 90 may also measure the hydrogen concentration of the hydrogen gas inside RHE[B].

[0046] The control means 91 controls the amount of hydrogen generated by controlling the current supplied to the water electrolysis cell of the polymer electrolyte water electrolysis apparatus 1 based on the hydrogen concentration of the hydrogen gas measured by the gas concentration measuring means 90, thereby controlling the amount of hydrogen gas supplied from the hydrogen supply system A. Specifically, as an example of the control form, if a reference value (lower limit) for the hydrogen concentration of the hydrogen gas is set in the control means 91, and the measured hydrogen concentration of the hydrogen gas input from the gas concentration measuring means 90 falls below this reference value, the current supplied to the water electrolysis cell of the polymer electrolyte water electrolysis apparatus 1 is increased to increase the amount of hydrogen generated and increase the amount of hydrogen gas supplied from the hydrogen supply system A. Increasing the amount of hydrogen supplied to RHE[B] in this way will also increase the hydrogen concentration of the hydrogen gas in RHE[B]. Subsequently, when the measured hydrogen concentration of the hydrogen gas input from the gas concentration measuring means 90 becomes equal to or above the reference value, the current supplied to the water electrolysis cell is returned to its original value to maintain a steady hydrogen generation rate.

[0047] Furthermore, the hydrogen concentration control mechanism 9 is not limited to this embodiment, as it only needs to be able to measure the hydrogen concentration of hydrogen gas inside the RHE[B] or hydrogen gas discharged from the RHE[B] and control the amount of hydrogen gas supplied from the hydrogen supply system A so that the measured hydrogen concentration is equal to or greater than a standard value. For example, various embodiments are possible, such as a mechanism in which the hydrogen generation amount of the water electrolysis cell is kept constant, and the hydrogen gas flow rate is controlled by a flow meter and pressure regulating valve installed in the lines supplying hydrogen gas from the water electrolysis cell to the RHE[B] (hydrogen supply lines 3, 6). The control means 82 constituting the liquid level holding mechanism 8 described above, and the control means 91 constituting the hydrogen concentration management mechanism 9, are implemented as functions of a microcomputer.

[0048] Next, the usage of the reference electrode system of this embodiment will be described. The usage of hydrogen supply system A is as described above. In the reference electrode system of this embodiment, hydrogen gas flowing through the hydrogen supply line 3 of the hydrogen supply system A is introduced into the RHE[B] from the gas inlet 231, discharged into the internal liquid 25 through the hydrogen gas introduction pipe 23, and then discharged to the gas exhaust line 14 from the gas outlet 26. When low-humidity hydrogen gas is introduced into the RHE[B], the internal liquid (water) of the RHE volatilizes and is discharged from the RHE[B] along with the hydrogen gas. If the amount of internal liquid (water) that volatilizes increases, the concentration and pH of the internal liquid of the RHE will change, and the accuracy of the potential measurement will decrease. Therefore, in order to perform stable potential measurements over a long period of time, it is desirable to maintain the liquid level of the internal liquid of the RHE[B] within a certain range. For this reason, the liquid level holding mechanism 8 measures the liquid level of the internal liquid of the RHE[B] and supplies water into the electrode so that the measured liquid level meets the reference value, thereby maintaining the liquid level of the internal liquid. That is, the liquid level of the internal liquid is measured continuously or at regular time intervals by the liquid level measuring means 80, and the measured value is sent to the control means 82. The control means 82 is configured to have, for example, a reference range for the internal liquid level (e.g., an initial setting value ±5%). When the liquid level measurement input from the liquid level measuring means 80 reaches the lower limit of the reference range, the control means 82 opens the on-off valve 812 of the water supply pipe 811 to supply water from the water supply tank 810 and maintain the internal liquid level. Then, when the liquid level measurement input from the liquid level measuring means 80 reaches the upper limit of the reference range, the control means 82 closes the on-off valve 812 to stop the water supply.

[0049] As mentioned earlier, the amount of water vapor evaporating from the internal liquid (moisture) of an RHE[B] varies depending on the balance between the hydrogen gas flow rate and the volume of internal liquid in the RHE, the installation environment (temperature, humidity), the test temperature (temperature of the internal liquid in the RHE), the structure of the RHE, etc., so it is not possible to say definitively how much water to supply. However, for example, in the case of an RHE with an internal liquid capacity of several tens of mL to 100 mL, depending on the operating environment, if it operates at room temperature and a hydrogen gas flow rate of about 0.1 mL / min to 1 mL / min is supplied, the amount of water to supply (replenishment) is thought to be several mL to several tens of mL / day. In the system of the present invention, the humidity of the hydrogen gas introduced is kept sufficiently low (preferably 1%RH or less), so the liquid level will not rise above the initial setting level when the system is started, and therefore only a water supply mechanism (liquid level holding mechanism 8) is required.

[0050] If gases other than hydrogen gas or contaminants enter the RHE[B] due to any factor, the potential of the RHE[B] will change, reducing the accuracy of potential measurement. Therefore, in order to perform stable potential measurement over a long period, it is desirable to always maintain an appropriate hydrogen gas concentration inside the RHE[B]. For this reason, the hydrogen concentration management mechanism 9 measures the hydrogen concentration of hydrogen gas inside the RHE[B] or hydrogen gas discharged from the RHE[B]. If the measured hydrogen concentration is below the standard value, it controls the solid polymer water electrolysis device 1 to increase the amount of hydrogen gas generated, thereby increasing the hydrogen concentration of hydrogen gas inside the RHE[B]. In other words, the hydrogen concentration of hydrogen gas flowing through the gas exhaust line 14 is measured continuously or at regular time intervals by the gas concentration measuring means 90, and the measured value is sent to the control means 91. The control means 91 is configured to have, for example, a reference value for the hydrogen concentration of the hydrogen gas (for example, a lower limit of 95 vol%). When the hydrogen concentration measurement value input from the gas concentration measuring means 90 falls below this reference value, the control means 91 increases the current value supplied to the water electrolysis cell of the polymer electrolyte water electrolysis device 1 to increase the amount of hydrogen generated. This increases the amount of hydrogen gas supplied from the hydrogen supply system A to RHE[B], thereby increasing the hydrogen concentration of the hydrogen gas inside RHE[B].

[0051] For example, at a steady level, the water electrolysis cell is energized with a current value such that the hydrogen generation rate is 0.1 mL / min or more and less than 1 mL / min for every 1 mL of internal liquid volume in the RHE[B]. However, when increasing the hydrogen generation rate as described above, the current is increased so that the hydrogen generation rate is 1 mL / min or more for every 1 mL of internal liquid volume in the RHE[B]. Then, when the hydrogen concentration measurement value input from the gas concentration measuring means 90 meets the reference value, the control means 91 returns the current value supplied to the water electrolysis cell of the polymer electrolyte water electrolysis apparatus 1 to its original value, and returns the hydrogen generation rate of the water electrolysis cell and the hydrogen gas supply rate to the RHE[B] to steady levels. As described above, by maintaining a constant liquid level of the internal liquid and hydrogen concentration of the hydrogen gas within the RHE[B] using the liquid level holding mechanism 8 and the hydrogen concentration control mechanism 9, there is no change in the potential of the RHE[B] itself, enabling stable potential measurement over a long period of time.

[0052] ≪Electrochemical Measurement Device≫ Next, the electrochemical measuring apparatus of the present invention, equipped with the reference electrode system (hydrogen supply system A + RHE[B]) described above, will be explained. The electrochemical measuring apparatus of the present invention is an apparatus equipped with the above-described reference electrode system, namely a hydrogen supply system A and an RHE[B] from which hydrogen gas is supplied from the hydrogen supply system A. Figure 6 shows a schematic representation of an electrochemical measuring device of the present invention equipped with the reference electrode system (hydrogen supply system A + RHE[B]) of Figure 3, including an electrochemical measuring cell and a reference electrode immersed in this cell (an explanatory diagram of the cell in a longitudinal cross-section). Here, the details of hydrogen supply system A and RHE[B] are as described in the embodiments of Figures 1 and 3, so a detailed explanation is omitted.

[0053] The electrochemical measuring device of this embodiment measures solution y (for example, "fluoride ions (F)"). - The apparatus comprises a cell 100 (test tank) containing an acidic aqueous solution (containing ) or an alkaline aqueous solution (), a reference electrode 101 and a counter electrode 102 immersed in the solution y in the cell 100, and when the apparatus is in use, the sample x (working electrode), which is the metal material to be tested, is also immersed in the solution y as shown in the figure. These configurations are the same as those of conventionally used known measuring devices. The reference electrode 101 is made of RHE and constitutes part of the reference electrode system of the present invention described above. Cell 100 is a beaker-shaped container with an open top, and a lid 103 is fitted over the top opening. The lid 103 has multiple mounting holes 104 through which the reference electrode 101 and counter electrode 102 are attached. The reference electrode 101, counter electrode 102, and sample x are inserted into cell 100 through the mounting holes 104 and supported by the lid 103 via a connector 105. In other words, the connector 105 serves to support the reference electrode 101, counter electrode 102, and sample x on the lid 103. The connector 105 also serves to close the upper end of the mounting holes 104 to prevent evaporation of the solution y. Furthermore, the lid 103 may have a mounting hole (not shown) for attaching a thermometer. The thermometer is inserted into the cell 100 through the mounting hole. By inserting the thermometer, the liquid temperature can be accurately evaluated, for example, when trying to control the liquid temperature. [Examples]

[0054] Using an electrochemical measurement device with RHE as the reference electrode, spontaneous potential measurement tests were conducted for up to 30 days. [Test Method] In this electrochemical measurement apparatus, a 1L glass five-neck separable flask was used as the electrochemical measurement cell. The solution was prepared by adding sulfuric acid dropwise to ultrapure water, adjusting the pH to 2 while checking the pH with a pH meter. 500 mL of the solution was placed in the electrochemical measurement cell, and an RHE, Pt wire, and thermometer were set in each of the three necks. The same pH 2 sulfuric acid solution was also placed in the RHE. The liquid temperature was controlled at 25°C using a constant temperature water bath. A gas inlet tube and a degassing tube were inserted into the remaining two necks of the electrochemical measurement cell, and before measurement, nitrogen gas was introduced into the liquid phase at a flow rate of 500 mL / min for 30 minutes to degas the cell. The gas phase was also degassed at a flow rate of 50 mL / min during the test. In this natural potential measurement test, the natural potential of Pt wires relative to RHE was measured for up to 30 days. A potentiostat (HZ-7000, manufactured by Meiden Hokuto Co., Ltd.) was used for potential measurement.

[0055] [Test conditions for Invention Example 1] RHE[B] conducted tests using the reference electrode system of the present invention equipped with a liquid level holding mechanism 8 (having the same configuration as the liquid level holding mechanism 8 in the embodiment shown in Figure 3). In this reference electrode system, a proton exchange membrane type water electrolysis cell was used for the solid polymer water electrolysis device of the hydrogen supply system. In this water electrolysis cell, iridium oxide IrOx (TEC77110, TKK) was hot-pressed on both sides of a Nafion membrane (N117, Dupont) as an oxygen evolution electrode catalyst, and platinum black was hot-pressed on both sides as a hydrogen evolution electrode catalyst to form a catalyst-coated membrane. The amount of each catalyst supported was 1 mg / cm³. 2 The electrode area is 4 cm². 2 The diffusion layer used a Pt-plated Ti fiber on the oxygen side and water-repellent treated carbon paper on the hydrogen side. Gold-plated titanium was used for the separator and SUS304 for the end plate, and a single cell was created by tightening the cell with bolts to 4 N·m. The separator was machined with parallel channels with a channel width and depth at 0.5 mm intervals. Ultrapure water was introduced to the oxygen electrode side of a single cell at a flow rate of 2 mL / min using a tubular pump, and a DC current of 0.04 A was supplied to the water electrolysis cell from a DC stabilized power supply to perform water electrolysis. The generated hydrogen gas was passed through a gas-liquid tank separator containing 200 mL of ultrapure water in a 500 mL PFA tank, and then introduced into the RHE. The hydrogen generation rate was set to 2 mL / min.

[0056] [Test conditions for Invention Example 2] A hydrogen concentration control mechanism 9 (having the same configuration as the hydrogen concentration control mechanism 9 in the embodiment shown in Figure 3) was added to the reference electrode system of the present invention used in Invention Example 1, and the same tests as in Invention Example 1 were carried out. [Test conditions for comparative examples] • Comparative Example 1 A glass RHE containing a hydrogen storage alloy cartridge, as shown in Figure 8, was used. • Comparative Example 2 This is the most common hydrogen supply system for RHE (Rotary Heater), where hydrogen gas, whose pressure and flow rate were adjusted by a regulator and flow meter, was supplied to the RHE from a high-pressure hydrogen cylinder. The hydrogen supply rate was set to 2 mL / min.

[0057] [Test Results] Figure 7 shows the potential measurement results of the Pt line in the inventive example and the comparative example. In Invention Examples 1 and 2, the natural potential of the Pt line remained stable at approximately 490 mV throughout the 30-day measurement period. In contrast, Comparative Example 1 also showed a stable natural potential of approximately 490 mV until the 25th day, but after the 25th day, the natural potential gradually increased, eventually reaching 520 mV. In Comparative Example 2, the initial potential was 490 mV, similar to Invention Examples 1 and 2 and Comparative Example 1, but after the 10th day, the potential dropped sharply, making measurement impossible.

[0058] Comparative Example 1 showed a potential equivalent to that of Invention Examples 1 and 2 against the Pt line until day 25, suggesting that it was functioning as a standard RHE. However, after day 25, the spontaneous potential gradually increased. This increase in potential midway through the test is thought to be due to a decrease or cessation of hydrogen supply from the hydrogen storage alloy, making it difficult for the oxidation-reduction reaction of hydrogen within the RHE to occur, thus destabilizing the potential measurement. When the hydrogen storage alloy cartridge removed from Comparative Example 1 was replaced with a new one and the same test was repeated, it again showed a stable potential of approximately 490 mV against the Pt line, confirming that there is a limit to the hydrogen capacity of the hydrogen storage alloy. The amount of hydrogen released from hydrogen storage alloys varies to some extent depending on the operating temperature (hydrogen is released more easily at higher operating temperatures), so in reality, there may be a certain degree of difference (for example, several days) in the period during which hydrogen can be supplied depending on the test conditions. However, for example, the "C-10 (III-3-3) Test Name: Potential Cycle (Load Response) Test Method" of the "NEDO PEFC Cell Evaluation and Analysis Protocol" mentioned above is a continuous test of approximately 28 days, so at least Comparative Example 1 cannot handle such a continuous test.

[0059] Furthermore, the sharp drop in potential after the 10th day in Comparative Example 2 is thought to be due to the evaporation of the internal solution (water) of the RHE and its discharge along with hydrogen gas, resulting in the concentration of the internal solution and a decrease in pH. In addition, the internal solution eventually ran out, making potential measurement impossible. Conventional electrochemical measurements are typically performed for a maximum of several tens of hours, and electrochemical measurements for longer periods are rarely conducted. As a result, this problem of evaporation of the internal solution (water) has not been recognized, but it was confirmed by Comparative Example 2. This natural potential measurement test, lasting up to 30 days, confirmed that the RHE can be operated stably even during long-term electrochemical measurements by using the hydrogen supply system and reference electrode system of the present invention. [Explanation of Symbols]

[0060] 1 Solid polymer water electrolysis device 2 Gas-liquid separator 3. Hydrogen supply line 4 Humidity adjustment mechanism 5. Gas Concentration Management Mechanism 6. Hydrogen supply line 7 Cooler 8 Liquid level retention mechanism 9. Hydrogen Concentration Management Mechanism 10 Solid polymer membrane 11 Catalyst layer 12 Diffusion layer 13 Separator 14 Gas exhaust line 15 Supply Tank 16. Liquid transfer pump 17. Fluid delivery line 18 Return Line 20 Support tube 21 Platinum electrode 22 Platinum conductor wire 23 Hydrogen gas inlet pipe 24. Ceramic porous material 25 Internal fluid 26 Gas outlet 40 Humidity measuring means 41 Hydrogen return line 42 Switching valve 43 Control means 50 Gas concentration measuring means 51 Gas exhaust section 52 Control means 80 Liquid level measuring means 81 Water supply means 82 Control means 90 Gas concentration measuring means 91 Control means 100 cells 101 Reference electrode 102 Opposite 103 Lid 104 mounting holes 105 Connector 230 Gas outlet 231 Gas inlet 810 Water tank 811 Water supply pipe 812 Shut-off valve A Hydrogen supply system B Reversible hydrogen electrode

Claims

1. A hydrogen supply system for supplying hydrogen to a reversible hydrogen electrode that constitutes the reference electrode of an electrochemical measuring device, A solid polymer water electrolysis device (1) that generates hydrogen gas by electrolyzing water, The hydrogen gas generated in the solid polymer water electrolysis apparatus (1) is introduced into a gas-liquid separator (2) that removes water contained in the hydrogen gas, A hydrogen supply system characterized by comprising a hydrogen supply line (3) for supplying hydrogen gas from which water has been removed by the gas-liquid separator (2) to a reversible hydrogen electrode.

2. Furthermore, the hydrogen supply system according to claim 1 is characterized by comprising a humidity control mechanism (4) that measures the humidity of the hydrogen gas flowing from the gas-liquid separator (2) to the hydrogen supply line (3) and adjusts the humidity of the hydrogen gas so that the measured humidity is below a standard value.

3. The humidity control mechanism (4) is A humidity measuring means (40) for measuring the humidity of hydrogen gas flowing through the hydrogen supply line (3), A hydrogen return line (41) is provided for returning hydrogen gas flowing through the hydrogen supply line (3) to the gas-liquid separator (2) from a position downstream of the humidity measurement position by the humidity measuring means (40) in the hydrogen supply line (3), A switching valve (42) that switches the line so that part or all of the hydrogen gas flowing through the hydrogen supply line (3) flows to the hydrogen return line (41), The hydrogen supply system according to claim 2, further comprising a control means (43) that controls the switching valve (42) based on the humidity of the hydrogen gas measured by the humidity measuring means (40) to divert some or all of the hydrogen gas flowing through the hydrogen supply line (3) to the hydrogen return line (41) and return it to the gas-liquid separator (2).

4. The hydrogen supply system according to claim 1, characterized in that the solid polymer water electrolysis apparatus (1) does not have a heating means and operates at room temperature.

5. Furthermore, the hydrogen supply system according to claim 1 is characterized by comprising a gas concentration management mechanism (5) that measures the hydrogen concentration of the hydrogen gas flowing through the hydrogen supply line (3) and exhausts the hydrogen gas flowing through the hydrogen supply line (3) to the outside of the line if the measured hydrogen concentration is below a standard value.

6. The aforementioned gas concentration control mechanism (5) is A gas concentration measuring means (50) for measuring the hydrogen concentration of hydrogen gas flowing through the hydrogen supply line (3), A gas exhaust section (51) is provided at a position downstream of the hydrogen concentration measurement position by the gas concentration measuring means (50) in the hydrogen supply line (3), where a switching valve is provided to exhaust the hydrogen gas flowing through the hydrogen supply line (3) to the outside of the line. The hydrogen supply system according to claim 5, further comprising a control means (52) that controls a switching valve of the gas exhaust section (51) based on the hydrogen concentration of the hydrogen gas measured by the gas concentration measuring means (50) to exhaust the hydrogen gas flowing through the hydrogen supply line (3) from the gas exhaust section (51).

7. The hydrogen supply system according to claim 1, characterized in that the hydrogen supply line (6) that sends the hydrogen gas generated in the solid polymer water electrolyzer (1) to the gas-liquid separator (2) is equipped with a cooler (7) that cools the hydrogen gas flowing through the line.

8. A reference electrode system for an electrochemical measuring device, characterized by comprising a hydrogen supply system (A) according to any one of claims 1 to 7, and a reversible hydrogen electrode (B) to which hydrogen gas is supplied from the hydrogen supply system (A).

9. The reference electrode system for an electrochemical measuring device according to claim 8, characterized in that the reversible hydrogen electrode (B) is provided with a liquid level holding mechanism (8) that measures the liquid level of the internal liquid in the electrode and supplies water into the electrode so that the measured liquid level meets a reference value, thereby maintaining the liquid level of the internal liquid.

10. The liquid level holding mechanism (8) is, A liquid level measuring means (80) for measuring the liquid level of the internal liquid, A water supply means (81) for supplying water into the electrode to maintain the liquid level of the internal liquid, A reference electrode system for an electrochemical measuring device according to claim 9, characterized in that it includes a control means (82) that controls the water supply means (81) to supply water into the electrode based on the liquid level measured by the liquid level measuring means (80).

11. Furthermore, the reference electrode system for an electrochemical measuring device according to claim 8 is characterized by comprising a hydrogen concentration management mechanism (9) that measures the hydrogen concentration of hydrogen gas inside the reversible hydrogen electrode (B) or hydrogen gas discharged from the reversible hydrogen electrode (B), and controls the amount of hydrogen gas supplied from the hydrogen supply system (A) so that the measured hydrogen concentration is equal to or greater than a reference value.

12. The hydrogen concentration control mechanism (9) is A gas concentration measuring means (90) for measuring the hydrogen concentration of hydrogen gas inside the reversible hydrogen electrode (B) or hydrogen gas discharged from the reversible hydrogen electrode (B), A reference electrode system for an electrochemical measuring device according to claim 11, characterized in that it includes a control means (91) for controlling the solid polymer water electrolysis device (1) to increase or decrease the amount of hydrogen gas generated based on the hydrogen concentration measured by the gas concentration measuring means (90).

13. An electrochemical measuring device characterized by comprising a hydrogen supply system (A) according to any one of claims 1 to 7, and a reversible hydrogen electrode (B) to which hydrogen gas is supplied from the hydrogen supply system (A).

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