WO2020203857A1

WO2020203857A1 - Hydrogen generation system

Info

Publication number: WO2020203857A1
Application number: PCT/JP2020/014240
Authority: WO
Inventors: 振王; 孝司松岡; 高見　洋史; 佐藤　康司; 小島　宏一; 直也伊藤; 拓辻村; 古谷　博秀
Original assignee: Ｊｘｔｇエネルギー株式会社
Priority date: 2019-03-29
Filing date: 2020-03-27
Publication date: 2020-10-08
Also published as: JP7229476B2; JP2020164942A

Abstract

A hydrogen generation system 40 is provided with: an electrolysis vessel 12 in which hydrogen is generated by the electrolysis of water; a direct-current power supply 14 which can supply an electrolytic current to the electrolysis vessel 12 by utilizing, as a direct current, an electric power sourced from a renewable energy input from an electric power generation device capable of generating an electric power sourced from a renewable energy; and a reverse current inhibition section 34 which can inhibit a reverse current I' generated in the electrolysis vessel 12 when the generation of an electric power sourced from the renewable energy is halted. The electrolysis vessel 12 is equipped with an electrode for oxygen generation use, an electrode for hydrogen generation use, and a solid polymer electrolyte membrane arranged between the electrode for oxygen generation use and the electrode for hydrogen generation use. The reverse current inhibition section 34 is arranged on a pathway through which the reverse current I' can flow.

Description

Hydrogen generation system

The present invention relates to a hydrogen generation system using renewable energy.

Conventionally, an electrochemical device using a solid polymer type ion exchange membrane has been devised as one of the devices for generating hydrogen. In this electrochemical device, oxygen and hydrogen are obtained by electrolysis of water by passing an electric current between the electrodes by a power source while supplying water to the anode. On the other hand, in such an electrochemical device, it is known that when the power supply is stopped, a reverse current is generated in the electrochemical cell, which deteriorates the electrode (see Patent Document 1).

Japanese Patent Application Laid-Open No. 1-222082

In recent years, renewable energy obtained from wind power, solar power, etc. has been attracting attention as an energy that can suppress carbon dioxide emissions in the production process compared to the energy obtained from thermal power generation. In addition, the development of a system using the above-mentioned electrochemical device or the like for the production of hydrogen using renewable energy is underway.

However, the output of a power generator that uses wind power or sunlight fluctuates frequently, and the output becomes zero depending on the windless weather or the weather. In this way, when a power generation device using wind power or solar power is used as a power source for an electrochemical device (for example, an electrolytic cell), the electrochemical device frequently stops and starts repeatedly. Therefore, when renewable energy is used as a power source, it is necessary to suppress the deterioration of the electrodes due to the irregular stoppage of the electrochemical device.

The electrochemical device as described above is generally operated continuously using stable electric power such as energy obtained by thermal power generation. Therefore, the stop of the electrochemical device is mainly when the power supply is intentionally stopped, and it is relatively easy to take measures against the deterioration of the electrode due to the stop of the electrochemical device. On the other hand, the problems in producing hydrogen by combining renewable energy and electrochemical equipment have not been fully investigated. As a result of diligent studies to realize realistic hydrogen production by combining renewable energy and an electrochemical device, the present inventors have found that electrode deterioration due to a large number of interruptions in the supply of renewable energy. I came up with a technology that suppresses and further improves the durability of electrochemical equipment.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a new technique for suppressing deterioration of electrodes in an electrolytic cell that electrolyzes water using electric power derived from renewable energy. To do.

In order to solve the above problems, the hydrogen generation system of one embodiment of the present invention converts an electrolytic cell that generates hydrogen by electrolysis of water and an electric current derived from the input renewable energy into the electrolytic cell. It includes a DC power source that supplies I, and a reverse current suppression unit that suppresses the reverse current I'generated in the electrolytic cell when the power generation device that generates power derived from renewable energy is stopped. The electrolytic cell has an oxygen-evolving electrode, a hydrogen-evolving electrode, and a solid polymer-type electrolyte membrane arranged between the oxygen-evolving electrode and the hydrogen-evolving electrode. The reverse current suppression unit is provided in a path through which the reverse current I'can flow.

According to the present invention, deterioration of electrodes in an electrolytic cell that electrolyzes water using electric power derived from renewable energy can be suppressed.

It is a schematic diagram which shows the schematic structure of the hydrogen generation system. It is a schematic diagram which shows the schematic structure of the electrolytic cell which concerns on 1st Embodiment. FIG. 3A is a diagram schematically showing a circuit configuration in which the hydrogen generation system is operating by input from the power generation device, and FIG. 3B is a diagram in which the input from the power generation device becomes zero and the hydrogen generation system is operated. It is a figure which shows typically the circuit structure after the stop. It is a figure which shows the change of the potential and the current after electrolysis stop. It is a schematic diagram which shows the circuit structure of the hydrogen generation system provided with the reverse current suppression part which concerns on 1st Embodiment. It is a figure which shows the change of the potential and the current after electrolysis stop in the hydrogen generation system provided with the reverse current suppression part which concerns on 1st Embodiment. It is a figure which shows the relationship between the number of times of stopping of the wind power generator which concerns on Example, and the life of an electrolytic cell. It is a figure which shows the probability of the cumulative number of stops with respect to the stop time of the wind power generator (300 kW) of Fukushima Renewable Energy Research Institute. 9 (a) and 9 (b) are diagrams showing an example of constant current measurement for measuring the electric capacity Q2 derived from the oxygen evolving electrode. It is a schematic diagram which shows the circuit structure of the hydrogen generation system provided with the reverse current suppression part which concerns on 2nd Embodiment. It is a figure which shows the change of the potential and the current after electrolysis stop in the hydrogen generation system provided with the reverse current suppression part which concerns on 2nd Embodiment.

First, the aspects of the present invention are listed. The hydrogen generation system of one aspect of the present invention includes an electrolytic cell that generates hydrogen by electrolysis of water, a DC power source that converts the input power derived from renewable energy and supplies an electrolytic current I to the electrolytic cell. It is provided with a reverse current suppression unit that suppresses the reverse current I'generated in the electrolytic cell when the power generation device that generates power derived from renewable energy is stopped. The electrolytic cell has an oxygen-evolving electrode, a hydrogen-evolving electrode, and a solid polymer-type electrolyte membrane arranged between the oxygen-evolving electrode and the hydrogen-evolving electrode. The reverse current suppression unit is provided in a path through which the reverse current I'can flow.

According to this aspect, the reverse current can be suppressed without providing a device for disconnecting the input between the power generation device and the DC power supply. Further, a reverse current suppression unit may be provided between the electrolytic cell and the DC power supply, or a reverse current suppression unit may be provided inside the electrolytic cell or the DC power supply.

The electric capacity Q1 calculated from the reverse current I'generated in the electrolytic tank between the time when the power generation by the power generation device is stopped and the elapse of T seconds (T> 0), and the electricity of the hydrogen generation electrode and the oxygen generation electrode. The electric capacity Q2 derived from the electrode having a small capacity satisfies the equation Q1 ≦ Q2 (where Q1 is ∫I ′ · dt (0 ≦ t ≦ T)).

The reverse current suppression unit may include a relay that switches on / off of the path through which the reverse current I'flows, and a control unit that controls the on / off of the relay. The control unit may operate the relay T seconds after the power generation by the power generation device is stopped to open the circuit. Alternatively, the control unit may activate the relay to open the circuit when the power generation by the power generation device is stopped. As a result, if the power generation device resumes power generation within T seconds after the power generation by the power generation device is stopped, the on / off control of the relay becomes unnecessary and the life of the relay is improved.

The reverse current suppression unit detects the voltage between the relay that switches the path through which the reverse current I'flows on / off, the control unit that controls the on / off of the relay, and the oxygen-evolving electrode and the hydrogen-generating electrode. It may have a voltage detection unit and a voltage detection unit. In the control unit, from the time when the power generation by the power generator is stopped until the potential of the oxygen generating electrode estimated from the voltage detected by the voltage detecting unit falls below the redox equilibrium potential of the catalyst of the oxygen generating electrode. In the meantime (before falling), the relay may be activated to open the circuit. Alternatively, in the control unit, after the power generation by the power generation device is stopped, until the potential of the hydrogen generation electrode estimated from the voltage detected by the voltage detection unit exceeds the redox equilibrium potential of the catalyst of the hydrogen generation electrode. In the meantime (before exceeding), the relay may be activated to open the circuit. As a result, deterioration of the electrode due to reverse current can be suppressed.

The reverse current suppression unit includes a relay that switches on / off of the path through which the reverse current I'flows, a control unit that controls on / off of the relay, and a potential detection unit that detects the potential of the oxygen generating electrode. You may. The control unit operates the relay until the potential of the oxygen-evolving electrode detected by the potential detection unit falls below (before) the redox equilibrium potential of the catalyst of the oxygen-evolving electrode to open the circuit. It may be. Alternatively, the reverse current suppression unit may have a potential detection unit that detects the potential of the hydrogen generating electrode. In that case, the control unit operates the relay until the potential of the hydrogen generation electrode detected by the potential detection unit exceeds (before) the redox equilibrium potential of the catalyst of the hydrogen generation electrode. The circuit may be opened. As a result, deterioration of the electrode due to reverse current can be suppressed more reliably.

When the potential of the oxygen-evolving electrode is obtained from the voltage, it can be easily obtained by grasping the potential fluctuation of the hydrogen-evolving electrode using a reference electrode in advance.
Voltage = anodic potential-cathode potential As shown in the above equation, the voltage is the difference between the oxygen generation electrode potential and the hydrogen generation electrode potential. Therefore, if the potential fluctuation of the hydrogen generation electrode is known, the oxygen generation electrode The potential change of is required.

The reverse current suppression unit may have a diode provided in the path. The diode uses Q2 as the electric capacity derived from the electric capacity of the electrode with the smaller electric capacity among the hydrogen generating electrode and the oxygen generating electrode, and the reverse current generated in the electrolytic tank within T seconds after the power generation by the power generation device is stopped. 'I "the average value of the average value of the reverse bias current _{I R} of the diode _{I R'} I _{(I R} 'When _{= ∫I R · dt / T (} 0 ≦ t ≦ T)), I R' It may be configured to satisfy ≦ I ”(I” = Q2 / T), whereby deterioration of the electrode due to reverse current can be suppressed.

It should be noted that any combination of the above components and the conversion of the expression of the present invention between methods, devices, systems, etc. are also effective as aspects of the present invention. Further, an appropriate combination of the above-mentioned elements may be included in the scope of the invention for which protection by the patent is sought by the present patent application.

Hereinafter, the present invention will be described based on a preferred embodiment with reference to the drawings. The embodiments are not limited to the invention, but are exemplary, and all the features and combinations thereof described in the embodiments are not necessarily essential to the invention. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and redundant description will be omitted as appropriate. Further, the scale and shape of each part shown in each figure are set for convenience for ease of explanation, and are not limitedly interpreted unless otherwise specified. Further, even if the members are the same, the scale and the like may be slightly different between the drawings. In addition, when terms such as "first" and "second" are used in this specification or claims, they do not represent any order or importance unless otherwise specified, and have a certain structure and others. It is for distinguishing from the composition of.

(First Embodiment)
[Hydrogen generation system]
FIG. 1 is a schematic diagram showing a schematic configuration of a hydrogen generation system. The hydrogen generation system 10 includes an electrolytic tank 12 that generates hydrogen by electrolysis of water, a DC power supply 14 that extracts electric power derived from the input renewable energy as a direct current and supplies the electrolytic current I to the electrolytic tank 12. To be equipped. A solar power generation device 16 or a wind power generation device 18 that generates power derived from renewable energy is connected to the DC power source 14 of the hydrogen generation system 10.

The DC power supply 14 may be a DC / DC converter, and is a regulated DC power supply (DC / DC converter) for taking out the DC current output from the solar power generation device 16 after adjusting the voltage to the voltage of the electrolytic tank. You may. Further, the DC power supply 14 may be an AC / DC converter, and the AC current output from the wind power generator 18 may be rectified and converted into a DC current, and then the DC current may be taken out.

FIG. 2 is a schematic view showing a schematic configuration of an electrolytic cell according to the first embodiment. The electrolytic cell 12 according to the present embodiment is a solid polymer membrane (PEM: Polymer Electrolyte Membrane) type water electrolytic cell using an ion exchange membrane. The electrolytic cell 12 has an anode 20 as an oxygen-evolving electrode, a cathode 22 as a hydrogen-generating electrode, and a solid polymer electrolyte membrane 24 arranged between the anode 20 and the cathode 22.

The anode 20 has an anode catalyst layer 20a, an anode gas diffusion layer 20b, and a separator 20c. The cathode 22 has a cathode catalyst layer 22a, a cathode gas diffusion layer 22b, and a separator 22c. The anode catalyst layer 20a according to the present embodiment contains iridium oxide (IrO ₂ ) as a raw material. Further, the cathode catalyst layer 22a according to the present embodiment contains platinum (Pt) and carbon (C). The above-mentioned catalyst contained in each catalyst layer is an example, and may be another metal or metal compound.

The solid polymer electrolyte membrane 24 is not particularly limited as long as it is a material that conducts protons (H ⁺ ), and examples thereof include a fluorine-based ion exchange membrane having a sulfonic acid group. The separator 20c is formed with a flow path through which water and oxygen flow, and a conductive corrosion-resistant material is preferable. The separator 22c is formed with a flow path through which hydrogen flows, and a conductive corrosion-resistant material is preferable.

The reaction of water in the electrolytic cell 12 during electrolysis is as follows.
Electrolyte when the positive electrode (anode) _{_{^{reaction: 2H 2 O → O 2 +}}} 4H + + 4e -
Negative electrode (cathode) reaction during ^{^{electrolysis: 4H + + 4e - → 2H}} 2

At the anode 20, water is electrolyzed to generate oxygen, protons and electrons. Protons move through the polymer electrolyte membrane 24 toward the cathode 22. Oxygen is released to the outside through the flow path formed in the separator 20c, and electrons flow into the positive electrode of the DC power supply 14. At the cathode 22, hydrogen is generated by the reaction between the electrons supplied from the negative electrode of the DC power supply 14 and the protons that have moved through the solid polymer electrolyte membrane 24.

[Cause of reverse current generation]
FIG. 3A is a diagram schematically showing a circuit configuration in which the hydrogen generation system is operating by input from the power generation device, and FIG. 3B is a diagram in which the input from the power generation device becomes zero and the hydrogen generation system is operated. It is a figure which shows typically the circuit structure after the stop.

As shown in FIG. 3A, the DC power supply 14 is a direct current or alternating current derived from renewable energy such as a photovoltaic power generation device 16 or a wind power generation device 18 (hereinafter, the case of alternating current will be described, but even if it is a direct current. (Good) is input, the voltage is converted by the transformer 26, rectified by the bridge type diode 28, smoothed by the smoothing electrolytic capacitor 30, and the electrolytic current I as a direct current is supplied from the output terminal 32 to the electrolytic tank 12. .. This enables electrolysis of water using renewable energy.

On the other hand, in a power generation device using renewable energy such as a solar power generation device 16 and a wind power generation device 18, stoppage and start-up are frequently repeated depending on the weather. Therefore, as shown in FIG. 3B, when the power generation is stopped and the alternating current input to the hydrogen generation system 10 becomes substantially zero, the reverse current I'flowing from the electrolytic cell 12 toward the DC power supply 14 is generated. appear.

The causes of the reverse current I'are 1) the static electricity of the anode and the cathode in the electrolytic cell 12 is generated by charging the smoothing electrolytic capacitor 30 of the DC power supply 14 and 2) the reverse of the electrode reaction in normal water electrolysis. It is considered that the reaction proceeds and occurs when the smoothing electrolytic capacitor 30 is charged. In addition, depending on the specifications of the power supply device, a discharge circuit of an electrolytic capacitor, a voltage measuring device, or the like may be built in, and a reverse current may occur through these circuits.

The reverse reaction after the electrolysis of water in the electrolytic cell 12 is stopped is as follows.
Electrolysis stopped after the positive electrode (anode) _{^{reaction: O 2 + 4H + + 4e}} - → 2H 2 O
Negative electrode (cathode) reaction after the electrolytic _{^{Stop: 2H 2 → 4H + + 4e}} -

FIG. 4 is a diagram showing changes in potential and current after electrolysis is stopped. The cell voltage (L3) before the electrolysis is stopped exceeds the theoretical operating voltage (electrolysis voltage including enthalpy change) of 1.48V for water electrolysis, but immediately after the electrolysis is stopped, the cell is caused by the reverse current due to the discharge of the electric double layer. The voltage gradually drops from the theoretical operating voltage of 1.48V. After that, the cell voltage falls below the theoretical electrolytic voltage of water (electrolytic voltage not including the enthalpy change) of 1.23 V, and then the anodic potential (L1) gradually decreases due to the reverse reaction.

For example, in the graph shown in FIG. 4, the anodic potential is 0.9 Vvs. Become NHE. _IrO 2 ⁺ 4H ^{+ +} 4e of Ir contained in the anode catalyst layer 20a ^- ← → respect Ir + 2H ₂ O redox equilibrium potential in the reaction is a standard hydrogen electrode (NHE), be 0.926V (25 ℃, vs.NHE) , The anode potential is below 0.926V. On the other hand, when the AC input to the DC power supply 14 is resumed and the supply of the electrolytic current I to the electrolytic cell 12 is resumed, the anode 20 again exceeds the theoretical operating voltage of 1.48 V. When the input from the power generation device to the DC power supply 14 is repeatedly stopped and restarted in this way, a potential fluctuation across the redox equilibrium potential of the catalyst of the anode occurs at the anode, and as a result, the anode catalyst deteriorates.

Therefore, the inventors of the present application have focused on a technique for suppressing the reverse current that causes a voltage change of the electrode in order to suppress such deterioration of the electrode. Specific examples thereof include a reverse current suppression unit including a relay and a diode. In this embodiment, a relay will be described as an example.

FIG. 5 is a schematic diagram showing a circuit configuration of a hydrogen generation system including a reverse current suppression unit according to the first embodiment. As shown in FIG. 5, the hydrogen generation system 40 suppresses the reverse current I'generated in the electrolytic cell 12 when the power generation derived from the renewable energy is stopped and the electrolysis in the electrolytic cell 12 is stopped. The suppression unit 34 is provided.

The reverse current suppression unit 34 includes a mechanical relay 36 that switches the path between the electrolytic cell 12 and the DC power supply 14 on / off, and a control unit 38 that controls the on / off of the mechanical relay 36. .. The control unit 38 has a switch 38a for switching the energization of the coil 36a of the mechanical relay 36, and a power supply 38b for applying a voltage to the coil 36a. As the power source 38b, for example, a DC power source having a voltage of 24 V may be used. A solid state relay, which is a non-contact relay, may be used instead of the mechanical relay 36, which is a contact relay.

The control unit 38 may have a processor, or may control the switch 38a according to an instruction from the processor. The processor may be, for example, a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit). Also. The control unit 38 may have a storage unit such as a memory, or may control the processor by a program stored in the storage unit.

In the reverse current suppression unit 34, during electrolysis, the control unit 38 turns on the switch 38a and energizes the coil 36a, so that the switch 36b of the mechanical relay 36 is turned on and between the DC power supply 14 and the electrolytic cell 12. Path is conductive. As a result, the electrolytic current I is supplied from the DC power supply 14 to the electrolytic cell 12.

On the other hand, the reverse current suppression unit 34 is an anode acquired from the potential detection unit 42 that detects the operating (power generation) state information acquired from the photovoltaic power generation device 16 or the wind power generation device 18 or the potential of each electrode of the electrolytic cell 12. Based on the voltage information between the 20 and the cathode 22, the control unit 38 determines whether or not the electrode is likely to deteriorate. For example, in the power generation information acquired from the photovoltaic power generation device 16 and the wind power generation device 18, when it is confirmed that the power generation is stopped for a period exceeding a predetermined reference time, it may be determined that the electrodes are likely to deteriorate. Further, when the potential of the anode 20 or the cathode 22 acquired from the potential detection unit 42 exceeds a specific potential, or when the amount of electricity of the reverse current from the electrolytic cell 12 to the DC power supply 14 exceeds a predetermined threshold, the electrode May be judged to be a situation in which is likely to deteriorate. The potential detection unit 42 may be replaced with a voltage detection unit. When the control unit 38 determines that each electrode of the electrolytic cell 12 is likely to deteriorate, the switch 38a is turned off and the coil 36a is cut off to open the switch 36b. As a result, the reverse current I'from the electrolytic cell 12 to the DC power supply 14 is cut off.

In this way, the reverse current suppression unit 34 can suppress the reverse current I'even when the input from the power generation device that generates power derived from renewable energy to the DC power supply is not cut off. As a result, the reverse current I'can be suppressed without providing a device for disconnecting the input between the power generation device and the DC power supply 14.

Further, the reverse current suppression unit 34 according to the present embodiment may be provided in a path through which the reverse current I'can flow in a closed circuit including the electrolytic cell 12 and the DC power supply 14. As a result, not only the reverse current suppression unit 34 can be provided between the electrolytic cell 12 and the DC power supply 14, but also the reverse current suppression unit 34 can be provided inside the electrolytic cell 12 and the DC power supply 14.

FIG. 6 is a diagram showing changes in potential and current after electrolysis is stopped in the hydrogen generation system provided with the reverse current suppression unit according to the first embodiment. As shown in FIG. 5, the control unit 38 that has detected the state in which the power generation in the power generation device has stopped shuts off the reverse current I'by opening the switch 36b in the mechanical relay 36. In this case, as shown in FIG. 6, the anodic potential (L1) is maintained at 1.1 V or higher. Since the anodic potential is not lower than the above-mentioned redox equilibrium potential of 0.926V, deterioration of the catalyst can be suppressed.

Further, in the case of the wind power generation device 18, depending on the weather, power generation is often stopped and restarted frequently. Therefore, the control unit 38 that has detected the state in which the power generation of the wind power generation device 18 has stopped can more reliably reduce the generation of the reverse current I'by immediately opening the mechanical relay 36. On the other hand, most of the wind power generation devices 18 have a short stop time for power generation (for example, a stop of 3 minutes or less). Therefore, if the reverse current I'does not occur between the stop and restart of the power generation by the power generation device, or even if the reverse current I'occurs, the deterioration of the electrodes is not significantly affected, the control unit 38 generates wind power. It is not necessary to immediately open the mechanical relay 36 even if the state in which the power generation of the device 18 is stopped is detected. Mechanical relays have a mechanical life (life for the number of times of opening and closing when no load is connected) and an electrical life (life for the number of times of opening and closing when load power is applied), but for all outages of wind power generators. When the mechanical relay is opened and closed, the consumption of the mechanical life is significantly increased. Therefore, by reducing the opening and closing of the mechanical relay, it is possible to reduce the frequency of replacement and select an inexpensive mechanical relay.

Therefore, the control unit 38 determines the potential of the anode 20 of the anode catalyst layer 20a after the power generation by the wind power generator 18 is stopped based on the voltage information between the anode 20 and the cathode 22 detected by the potential detection unit 42. The mechanical relay 36 may be operated to open the circuit until it falls below the redox equilibrium potential (0.926 V) (before it falls). As a result, deterioration of the anode 20 due to the reverse current I'can be suppressed more reliably. Further, if the wind power generator 18 resumes power generation until the potential of the anode 20 falls below the redox equilibrium potential of the anode catalyst layer 20a (before it falls below), the on / off control of the mechanical relay 36 becomes unnecessary. , The life of the mechanical relay 36 is improved.

On the other hand, in the case of the hydrogen generation system 40 in which the potential detection unit 42 is not provided, the control unit 38 operates the mechanical relay 36 T seconds after the power generation by the wind power generation device 18 is stopped (T> 0). The circuit may be opened. As a result, if the wind power generation device 18 resumes power generation within T seconds after the power generation by the wind power generation device 18 is stopped, the on / off control of the mechanical relay 36 becomes unnecessary, and the mechanical relay 36 Life is improved.

Next, the value of T to be set in advance will be described. Assuming that the life of the electrolytic cell 12 is determined by the deterioration of the electrode, the number of stops of the power generation device that causes the deterioration of the electrode due to the reverse current I'is important. The life due to deterioration of the electrodes is based on, for example, a case where the voltage during electrolysis of the electrolytic cell 12 (in the case of a current density of 1 A / cm ² ) increases by 20%.

In general, the wind power generation device 18 has a larger number of stops than the solar power generation device 16, so the following description will focus on the number of stops of the wind power generation device 18. FIG. 7 is a diagram showing the relationship between the number of times the wind power generator is stopped per day and the life of the electrolytic cell according to the embodiment. For example, if the number of stops is 120 times / day, the life of the electrolytic cell is 2.1 years, if the number of stops is 50 times / day, the life of the electrolytic cell is 5 years, and if the number of stops is 25 times / day, the life of the electrolytic cell is 10. If the number of stops is 12.5 times / day, the life of the electrolytic cell will be 20 years.

Here, the stop counted as the number of stops is a stop having a length that affects the life of the electrolytic cell. For example, a stop of several seconds to several tens of seconds has a reverse current I that affects the deterioration of the electrode. 'Almost never occurs. In other words, if the reverse current I'that affects the deterioration of the electrodes does not occur, it is not always necessary to cut off the reverse current I'when the wind power generator is stopped for a short time.

Therefore, a short stop (stop until T seconds after the stop of power generation) of the wind power generator that does not generate a reverse current I'that affects the deterioration of the electrodes is not counted in the number of stops. Will also be good. Specifically, if the number of stops from the stop of power generation to T seconds later is 70 times / day, the actual number of stops that actually affects the life of the electrolytic cell is 120-70 = 50 times / day. (The number of stops is reduced by about 58%), and the life of the electrolytic cell is extended to about 5 years.

Similarly, if the number of stops from the stop of power generation to T seconds later is 95 times / day, the actual number of stops that actually affects the life of the electrolytic cell is 120-95 = 25 times / day (stops). The number of times is reduced by about 79%), and the life of the electrolytic cell is extended to about 10 years. Further, if the number of stops from the stop of power generation to T seconds later is 107.5 times / day, the actual number of stops that actually affects the life of the electrolytic cell is 120-107.5 = 12.5. The number of times / day is reduced (the number of stops is reduced by about 90%), and the life of the electrolytic cell is extended to about 20 years.

FIG. 8 is a diagram showing the probability of the cumulative number of outages with respect to the outage time of the wind power generator (300 kW) of the Fukushima Renewable Energy Research Institute. In this wind power generator, outages of up to 600 seconds account for 93% of the total. In a wind power generator in such a usage environment, if an attempt is made to reduce the actual number of stops by about 58%, as shown in FIG. 8, a reverse current I'that affects the deterioration of the electrodes when stopped for up to 54 seconds. Should not occur. Further, in order to reduce the actual number of stops by about 79%, as shown in FIG. 8, it is sufficient that the reverse current I'that affects the deterioration of the electrode does not occur at the stop for up to 142 seconds.

[Measurement of T (time since power generation stopped) that affects electrode deterioration]
The electric capacity Q1 = ∫I' · dt (0 ≦ t ≦ T) calculated from the reverse current I ′ generated in the electrolytic cell 12 within T seconds after the power generation by the power generation device is stopped. The reverse current I'can be easily measured with a DC ammeter, a clamp meter (overhead wire ammeter), or the like. When measuring reverse current with a DC ammeter, the DC ammeter must be fixedly installed between the electrolytic tank and the DC power supply, and must withstand the current during operation of the electrolytic tank and also measure weak reverse current. It is a high-cost device. On the other hand, with a clamp meter (overhead ammeter) that does not need to be installed in the circuit, the device can be selected exclusively for the weak reverse current, so the reverse current can be measured inexpensively and accurately. , A more desirable form. The electric capacity Q2 derived from the anode 20 can be obtained in advance by the following constant current measurement after the electrolytic cell is stopped. The conditions for constant current measurement and the composition of the electrolytic cell are as follows.

Cell temperature: 25 ° C
Current density: -0.2mA / cm ² (current in the opposite direction to normal electrolysis)
Tripolar electrolytic cell: cathode, anode, reference electrode (standard hydrogen electrode, NHE)
Cathode catalyst: Platinum-supported carbon (Pt / C)
Anode catalyst: Iridium oxide Electrode area: 25 cm ²
After performing the water electrolysis test at + 1 A / cm ² for 3 hours, the electrolytic cell was temporarily stopped, and immediately after that, a reverse current was forcibly flowed at −0.2 mA / cm ² using an electrochemical measuring device. The anode potential from the reference electrode was measured, and the electric capacity up to the redox potential of the anode was measured.

9 (a) and 9 (b) are diagrams showing an example of the above-mentioned constant current measurement for measuring the electric capacity Q2 derived from the oxygen evolving electrode. The redox potential of the anode-catalyzed iridium oxide used this time was 0.926 V vs. as described above. NHE (NHE potential ≈ RHE potential because pH ≈ 1). In this example, the electric capacity Q2 was 1170 mC (46.8 mC / cm ² ).

The electric capacity Q2 slightly changes depending on the current density of the reverse current. In this test, the rated 1A / cm ^2, since the current density is -0.2mA / cm ^2, current density is 1/5000 of the rated. The current density of the reverse current for accurately measuring the electric capacity Q2 is 1/100 or less, more preferably 1/10000 to 1/1000, with respect to the absolute value of the rated current of water electrolysis. When measured with a current value larger than 1/100, accurate electric capacity Q2 cannot be measured due to voltage loss due to ion transfer resistance or the like.

When the electric capacities Q1 and Q2 calculated as described above satisfy Q1 ≦ Q2, the reverse current I ′ that affects the deterioration of the electrode does not occur. In that case, the control unit 38 operates the mechanical relay 36 T seconds after the input from the power generation device becomes zero to open the circuit. As a result, deterioration of the electrode due to the reverse current I'can be suppressed.

In this example, since iridium oxide was used as a catalyst, 0.926V (vs. NHE) was used as the standard electrode potential (E ⁰ ) for redox, but when other catalysts were used, the respective catalysts were used. The electric capacity Q2 can be calculated by changing to the standard electrode potential for redox. The standard electrode potential of a typical catalyst is as follows.
RuO ₂ + 4H ⁺ + 4e → Ru + 2H ₂ O E ⁰ = 0.68V
^{PtO + 2H + + 2e → Pt} + H 2 O E 0 = 0.98V
NiO ₂ + 2H ₂ O + 2H ⁺ + 2e → 2Ni (OH) ₂ E ⁰ = 1.032V

The standard electrode potential indicates the oxidation-reduction potential at 25 ° C., but when it is assumed that the electrolytic cell temperature at the time of stopping is high, it is desirable to correct the temperature by the Nernst equation. The redox involved in this degradation mode is a redox reaction pair between 0V and 1.23V and a redox reaction pair between 0.1V and 1.1V at the assumed temperature. Especially effective in the case. Since the potentials of the anode and the cathode during the stoppage are 0 V or more and 1.23 V or less, there is no control effect on the redox reaction pair outside this range. Further, when there is a redox reaction pair at 0.1 V or more and 1.1 V or less, the amount of reduction in the number of times the relay is opened and closed is large, and the effect is more likely to be exhibited.

In the above explanation, the decrease in anodic potential due to the reverse current generated at the time of stopping was described. The electric capacity derived from the cathode (hydrogen generation electrode) and anode (oxygen generation electrode) of the electrolytic cell varies greatly depending on the catalyst type, catalyst carrier type, catalyst amount, and the like. When the cathode electric capacity is larger than the anode electric capacity, the anode potential decreases as described above, but when the cathode electric capacity is smaller than the anode electric capacity, the cathode potential increases. In this case as well, it is necessary to control so that the potential fluctuation across the redox equilibrium potential of the cathode catalyst does not occur, as in the case of the decrease in the anode potential. That is, it is necessary to operate the relay to open the circuit until the redox equilibrium potential of the catalyst of the cathode (hydrogen generation electrode) is exceeded (before it is exceeded). As a result, it is possible to suppress deterioration of the cathode and reduce the number of times the relay is opened and closed.

(Second Embodiment)
In this embodiment, a diode is used as the reverse current suppression unit. FIG. 10 is a schematic diagram showing a circuit configuration of a hydrogen generation system including a reverse current suppression unit according to the second embodiment. As shown in FIG. 10, the hydrogen generation system 50 suppresses the reverse current I'generated in the electrolytic cell 12 when the power generation derived from the renewable energy is stopped and the electrolysis in the electrolytic cell 12 is stopped. The suppression unit 34 is provided. The reverse current suppression unit 34 is provided in the middle of the path between the electrolytic cell 12 and the DC power supply 14, and includes a diode 34a having a predetermined characteristic.

Here, attention is focused on the reverse bias current _{I R} as characteristic of the diode 34a. The diode 34a according to the present embodiment has an electric capacity derived from the electric capacity of the anode 20 Q2 (cathode electric capacity> anode electric capacity), and is generated in the electrolytic tank within T seconds after the power generation by the power generation device is stopped. 'the mean value of I ", the average value of the reverse bias current _{I R} of the diode _{I R'} reverse current I When _{_{(I R '= ∫I R ·}} dt / T (0 ≦ t ≦ T)), I R It is configured to satisfy'≤I" (I "= Q2 / T).

As described above, when renewable energy is used as a power source, a short stop is dominant, so it is desirable to select a diode that suppresses these. For example, in the wind power generator (300 kW) of the Fukushima Renewable Energy Research Institute shown in FIG. 8, 93% stoppage is within 600 seconds, so by selecting a diode with T as 600 seconds, 93% It is possible to avoid deterioration due to the stoppage of. Incidentally, a reverse bias current I _R is selected very small diodes, can also avoid degradation due to stop more than a few hours, increasing the cost of the diode itself, cost advantage as a total is reduced.

FIG. 11 is a diagram showing changes in potential and current after electrolysis is stopped in the hydrogen generation system provided with the reverse current suppression unit according to the second embodiment. As shown in FIG. 11, when the power generation in the power generation device is stopped and the electrolysis in the electrolytic cell 12 is also stopped, the anodic potential is maintained at about 1.0 V without any particular control. Thus, the reverse bias current I _R can be suppressed and deterioration of the electrode is also due to the reverse current with the diode in a predetermined range.

Further, when the cathode electric capacity is smaller than the anode electric capacity, the cathode potential rises, but as in the case of the relay, the potential fluctuation across the oxidation-reduction equilibrium potential of the cathode catalyst is prevented from occurring at the cathode. It is necessary to control. In this case, it is possible to obtain the same effects as the anode by determining the reverse bias current I _R the capacitance derived from the cathode as Q2.

Although the present invention has been described above with reference to each of the above-described embodiments, the present invention is not limited to the above-described embodiments, and the present invention is not limited to the above-described embodiments, and the configurations of the embodiments are appropriately combined or replaced. Is also included in the present invention. Further, it is also possible to appropriately rearrange the combination and the order of processing in the embodiment based on the knowledge of those skilled in the art, and to add modifications such as various design changes to the embodiment, and such modifications are added. Such embodiments may also be included in the scope of the present invention.

In the hydrogen generation system according to each of the above-described embodiments, an example is used in which an alternating current derived from renewable energy is converted to direct current by a transformer, smoothed by a smoothing electrolytic capacitor, and then supplied to an electrolytic cell as an electrolytic current. Although explained, it is not necessarily limited to this example. For example, a direct current power source that supplies a direct current derived from renewable energy to an electrolytic cell as an electrolytic current after voltage conversion with a DC-DC converter and smoothing with a smoothing electrolytic capacitor may be used.

The present invention can be used for a hydrogen generation system using renewable energy.

10 Hydrogen generation system, 12 Electrolyte tank, 14 DC power supply, 16 Solar power generation device, 18 Wind power generation device, 20 Anode, 20a Anode catalyst layer, 20b Anode gas diffusion layer, 20c Separator, 22 Cathode, 22a Cathode catalyst layer, 22b Cathode gas diffusion layer, 22c separator, 24 solid polymer electrolyte membrane, 34 reverse current suppression unit, 34a diode, 36 mechanical relay, 38 control unit, 40 hydrogen generation system, 42 potential detection unit, 50 hydrogen generation system.

Claims

An electrolytic cell that generates hydrogen by electrolysis of water,
A DC power source that supplies an electrolytic current I to the electrolytic cell using the power derived from the renewable energy input from the power generation device that generates power derived from the renewable energy as a direct current.
A reverse current suppression unit that suppresses the reverse current I'generated in the electrolytic cell when the power generation device is stopped is provided.
The electrolytic cell has an oxygen-evolving electrode, a hydrogen-evolving electrode, and a solid polymer-type electrolyte membrane arranged between the oxygen-evolving electrode and the hydrogen-generating electrode.
The hydrogen generation system is characterized in that the reverse current suppression unit is provided in a path through which the reverse current I'can flow.
The electric capacity Q1 calculated from the reverse current I'generated in the electrolytic tank between the time when the power generation by the power generation device is stopped and the elapse of T seconds (T> 0) is ∫I' · dt (0 ≦ t ≦). T), the electric capacity Q2 derived from the electrode for generating hydrogen and the electrode for generating oxygen having a small electric capacity and the electric capacity Q1 satisfy the formula Q1 ≦ Q2. The hydrogen generation system according to 1.
The reverse current suppression unit includes a relay that switches on / off of the path through which the reverse current I'flows, and a control unit that controls on / off of the relay.
The hydrogen generation system according to claim 2, wherein the control unit operates the relay T seconds after the power generation by the power generation device is stopped to open the circuit.
The reverse current suppression unit includes a relay that switches on / off of the path through which the reverse current I'flows, and a control unit that controls on / off of the relay.
The hydrogen generation system according to claim 2, wherein the control unit operates the relay to open the circuit when the power generation by the power generation device is stopped.
The reverse current suppressing unit includes a relay that switches on / off of the path through which the reverse current I'flows, a control unit that controls on / off of the relay, and an oxygen generating electrode and a hydrogen generating electrode. It has a voltage detector that detects the voltage between them, and
The control unit performs the relay after the power generation by the power generation device is stopped and before the potential of the oxygen generating electrode estimated from the voltage falls below the redox equilibrium potential of the catalyst of the oxygen generating electrode. The hydrogen evolution system according to claim 1 or 2, wherein the circuit is opened by activating.
The reverse current suppressing unit includes a relay that switches on / off of the path through which the reverse current I'flows, a control unit that controls on / off of the relay, and an oxygen generating electrode and a hydrogen generating electrode. It has a voltage detector that detects the voltage between them, and
The control unit performs the relay after the power generation by the power generation device is stopped and before the potential of the hydrogen generation electrode estimated from the voltage exceeds the redox equilibrium potential of the catalyst of the hydrogen generation electrode. The hydrogen generation system according to claim 1 or 2, wherein the hydrogen generation system is operated to open a circuit.
The reverse current suppression unit includes a relay that switches on / off of the path through which the reverse current I'flows, a control unit that controls on / off of the relay, and a potential detection unit that detects the potential of the oxygen generating electrode. And have
The control unit operates the relay to open the circuit before the potential of the oxygen-evolving electrode detected by the potential detection unit falls below the redox equilibrium potential of the catalyst of the oxygen-evolving electrode. The hydrogen evolution system according to claim 1 or 2, characterized in that.
The reverse current suppression unit includes a relay that switches on / off of the path through which the reverse current I'flows, a control unit that controls on / off of the relay, and a potential detection unit that detects the potential of the hydrogen generating electrode. And have
The control unit operates the relay to open the circuit before the potential of the hydrogen generation electrode detected by the potential detection unit exceeds the redox equilibrium potential of the catalyst possessed by the hydrogen generation electrode. The hydrogen generation system according to claim 1 or 2, characterized in that.
The reverse current suppression unit has a diode provided in the path and has a diode.
The diode has an electric capacity derived from the electrode having a smaller electric capacity among the hydrogen generating electrode and the oxygen generating electrode Q2, and is generated in the electrolytic tank within T seconds after the power generation by the power generating device is stopped. 'I "the average value of the average value of the reverse bias current I R of the diode I R' wherein reverse current I When (I R '= ∫I R · dt / T (0 ≦ t ≦ T)), I R '≦ I "(I " = Q2 / T) hydrogen generation system according to claim 2, characterized in that it is configured to satisfy.