JP2000026986A - Solid electrolyte type water electrolysis apparatus and water electrolysis method using the apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte type water electrolysis apparatus capable of efficiently executing water electrolysis with low voltage without entailing an increase of electrolytic voltage and a water electrolysis method using the apparatus. SOLUTION: The water electrolysis is effected at 60 to 120 deg.C by using the solid electrolyte type water electrolysis apparatus consisting of an electrolytic cell 1 constituted by plating a platinum group metal on both surfaces of a solid electrolyte membrane 2, disposing porous power feeders 3 on both sides of the solid electrolyte membrane 2 and disposing electrode plates 4 on the outer side of the respective porous power feeders 3 and using Ir or Ru as the platinum group metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte type water electrolysis apparatus and a water electrolysis method using the apparatus.

[0002]

2. Description of the Related Art First, a water electrolysis method using a solid electrolyte membrane will be described for understanding the present invention. For example, water electrolysis can be performed by a solid electrolyte type water electrolysis apparatus having an electrolysis cell as shown in FIG. In FIG. 1, an electrolytic cell 1 is provided with a solid electrolyte membrane 2, porous feeders 3, 3 attached to both surfaces of the solid electrolyte membrane 2, and disposed outside the porous feeders 3, 3. Electrode plates 4 and 4. 5 is an annular gasket, 6 is a fastener. The solid electrolyte membrane 2 is a solid polymer electrolyte membrane made of a proton conductive material, and is preferably a cation exchange membrane (a fluororesin sulfonic acid cation membrane, for example, “Nafion 117” manufactured by DuPont). On both surfaces of the solid electrolyte membrane 2, a porous metal thin film made of a platinum group metal is plated. The porous power supply 3 is made of a conductive mesh made of titanium or the like.

The upper side of the electrolytic cell 1 having such a structure is an anode.
The chamber is energized so that the lower side is the cathode chamber, and pure water 7 is
If supplied to the anode chamber, 2H_Two0 → 0_Two+ 4H⁺+ 4e^- Reaction occurs, and oxygen gas is generated. Generated in the anode compartment
The protons flow through the proton conductive solid electrolyte membrane 2.
It travels with a small amount of water and reaches the cathode compartment. In the cathode compartment
Is the 4H⁺+ 4e^-→ 2H_Two  Reaction occurs, and hydrogen gas is generated. Like this
Water electrolysis is performed to generate oxygen gas and hydrogen gas
However, the electrolytic cell voltage at this time is
expressed.

[0004] V = Vt + Va + Vc + IR where V is the electrolytic cell voltage, Vt is the theoretical decomposition voltage, Va
Is overvoltage on the anode side, Vc is overvoltage on the cathode side, IR is solid
It represents ohmic loss such as resistance of the electrolyte membrane.

In order to reduce the production cost of hydrogen and oxygen in the water electrolysis method, it is necessary to lower the voltage of the electrolytic cell. The respective voltages for determining the electrolysis cell voltage will be described below.

[0006] Vt is theoretically determined, and at ambient temperature it is 1.
23 V, but decreases as the electrolysis temperature increases.

Vc is almost constant and is about 0.1V.
IR is determined by the structure of the electrolytic cell, the material used for the electrolytic cell, the method of assembling the electrolytic cell, and the like.

[0008] Va is determined by the type of platinum group metal to be plated on the solid electrolyte membrane. For example, Ir and Ru can reduce Va as compared with platinum. However,
Since Ir and Ru are dissolved in pure water, the voltage of the electrolytic cell may increase, and particularly in the case of a water electrolyzer having a large number of on / off times, plated Ir or Ru elutes in a short time. . If the electrolysis is continued in this state, the plating layer of Ir or Ru becomes thin, and Va increases, that is, the electrolytic cell voltage increases, so that the cost of hydrogen / oxygen generation power increases significantly.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to carry out water electrolysis efficiently at a low voltage without increasing the voltage of the electrolytic cell. An object of the present invention is to provide a solid electrolyte type water electrolysis device that can be performed and a water electrolysis method using the device.

[0010]

In order to achieve the above-mentioned object, the present invention provides a solid electrolyte membrane in which a metal or an oxide is plated on both sides, and a porous feeder is arranged on both sides of the solid electrolyte membrane. In a solid electrolyte type water electrolysis apparatus comprising an electrolytic cell having an electrode plate disposed outside each porous power supply, the metal or oxide is a platinum group metal or an alloy thereof or an oxide thereof having an anode overvoltage lower than platinum. The first invention is a solid electrolyte type water electrolysis apparatus characterized by comprising a heating means for pure water for water electrolysis, and in the first invention,
The second invention is a solid electrolyte type water electrolysis apparatus characterized in that the platinum group metal is Ir or Ru. In the first or second invention, it is preferable that the solid electrolyte membrane is a solid polymer electrolyte membrane. A solid electrolyte type water electrolysis device characterized by the third invention, a platinum group metal having a lower anode overvoltage than platinum or an alloy or oxide thereof is plated on both surfaces of the solid electrolyte membrane, and on both sides of the solid electrolyte membrane Using a solid electrolyte type water electrolysis apparatus comprising an electrolytic cell in which a porous feeder is disposed and an electrode plate disposed outside each porous feeder, pure water is heated to a high temperature in advance, and then water electrolysis is performed. A fourth aspect of the present invention is the water electrolysis method, wherein the platinum group metal is Ir or Ru in the fourth invention. In the invention of A sixth aspect of the present invention is a water electrolysis method characterized in that the temperature of electrolysis is 60 to 120 ° C., and in the fourth, fifth or sixth invention, the solid electrolyte membrane is a solid polymer electrolyte membrane. A featured water electrolysis method is a seventh invention.

FIG. 6 shows the relationship between the above voltages when the current density is plotted on the horizontal axis and the electrolytic cell voltage is plotted on the vertical axis. The electrolysis temperature at this time is 25 ° C.

Since Vc is constant and ohmic loss inevitably occurs, in order to lower the electrolysis cell voltage, the electrolysis temperature must be increased to lower Vt, or Vt must be lowered.
It is necessary to plate the solid electrolyte membrane with a platinum group metal having a low a (for example, Ir or Ru).

Therefore, when the electrolysis temperature is maintained at 30 ° C. and the electrolysis is continued at an electrolysis current density of 1.4 A / cm ² using an electrolysis cell incorporating a solid electrolyte membrane plated with Ir having a lower Va than Pt, FIG. As shown in FIG. 7, the electrolysis cell voltage increased with time. When the electrolytic current density was increased from the above value, the rate of increase of the electrolytic cell voltage was increased. Therefore, when compared at the same electrolytic current density, the rate of increase in the electrolytic cell voltage was higher when the pure water temperature was lower than when it was higher. However, Pt did not show such an increase in the electrolytic cell voltage.

Next, when water electrolysis was performed using an electrolytic cell incorporating a solid electrolyte membrane plated with Ru having a lower Va than Ir, the increase in the electrolytic cell voltage was larger than that in the case of Ir.

That is, a platinum group metal having a low Va (I)
The use of a solid electrolyte membrane plated with (r or Ru) alone increases the voltage of the electrolytic cell. Therefore, in order to keep the voltage of the electrolytic cell low, a solid electrolyte membrane plated with a platinum group metal with low Va (Ir or Ru) must be used. It can be seen that it is necessary to perform electrolysis while increasing the electrolysis temperature while using.

In general, when performing electrolysis, not all of the electric energy supplied to the electrolysis cell is used for electrolysis, and part of the electric energy is consumed for raising the temperature of pure water. For this reason,
As the water electrolysis is continued, the temperature of the pure water gradually increases. However, when the size of the water electrolyzer is large, it takes a long time to raise the temperature.

Therefore, when water electrolysis is performed at a high electrolysis current density, the temperature of pure water also rises in a short time, but the rise of the electrolysis cell voltage also increases. Conversely, when water electrolysis is performed at a low electrolysis current density, the increase in the electrolysis cell voltage is small, but it takes a long time to raise the temperature of pure water, which is not efficient. Therefore, when the pure water for electrolysis is heated in advance using the heating means of the solid electrolyte type water electrolysis apparatus of the present invention, and the electrolysis is started after the electrolysis temperature is raised, the electrolysis cell voltage is kept low, and the electrolysis is performed. Water electrolysis can be performed at a low voltage without increasing the voltage even if the continuation is continued. For this purpose, the electrolysis temperature is preferably set to 60 ° C. or higher, but the upper limit of the electrolysis temperature is set to 120 ° C. in consideration of the heat resistance of the equipment constituting the water electrolysis apparatus and the solid electrolyte membrane.
It is preferred that

For example, while maintaining the electrolysis temperature at 80 ° C.,
FIG. 2 shows the time course of the electrolytic cell voltage when water electrolysis was carried out using a water electrolysis apparatus in which was plated on a solid electrolyte membrane.
As shown in the figure, the electrolysis cell voltage (V) slightly increases at the beginning of electrolysis, but thereafter keeps a substantially constant value. That is, Ir elutes at the beginning of electrolysis, but then stops eluting. As described above, when the electrolysis is started with the electrolysis temperature raised, the electrolysis voltage slightly rises at the beginning of electrolysis and then maintains a substantially constant value at a voltage lower than the case of the electrolysis temperature of 30 ° C. Water electrolysis can be performed at a current density. For this purpose, instead of using a part of the electric energy supplied to the electrolytic cell to raise the temperature of the pure water in the water electrolyzer, a heating means such as an electric heater is provided in the water electrolyzer to raise the pure water. It is preferred to warm. After the temperature of the pure water is raised by the heating means, the operation of the heating means can be stopped. This is because part of the electric energy for water electrolysis is consumed for raising the temperature of pure water.

[0019]

Embodiments of the present invention will be described below. In this example, a solid polymer electrolyte membrane was used as the solid electrolyte membrane. FIG. 3 is an overall flowchart of one embodiment of the solid polymer electrolyte type water electrolysis device of the present invention. In FIG. 3, reference numeral 11 denotes the same as the electrolytic cell 1 shown in FIG. 1, and pure water reaches the electrolytic tank 12 again from the electrolytic tank 12 having the electrolytic cell 11 via the pump 13, the electric heater 14, and the heat exchanger 15. A circulation path 16 is formed. 17 is a supply path of makeup water. Electrolytic cell 1
From the upper anode chamber, pure water mist is discharged together with oxygen gas through a passage 18, and the pure water mist (moisture) in the oxygen gas is removed by a dehumidifier 19. From the cathode chamber below the electrolytic cell 11, pure water is discharged together with hydrogen gas through a passage 20, and the pure water and the hydrogen gas containing moisture are removed from the pure water in the gas in a hydrogen gas separation tank 21. It is separated and sent to the pump 13 via the path 22. Further, moisture in the hydrogen gas discharged from the hydrogen gas separation tank 21 via the path 23 is removed by the dehumidifier 24. 25 is a pressure regulating valve, 26 is a controller, which controls the pressure in the electrolytic tank 12 and the hydrogen gas separation tank 21.
When the internal pressure difference becomes equal to or greater than a predetermined value, the controller 26 opens the pressure regulating valve 25.

According to the water electrolysis apparatus configured as described above, water electrolysis can be performed as follows.

First, the electric heater 14 is energized, and the operation of the pump 13 is started so that the pure water in the electrolytic tank 12 flows through the pump 13, the electric heater 14 and the heat exchanger 15 to the circulation path 16 leading to the electrolytic tank 12. The temperature is raised while circulating. FIG. 4 is a diagram showing an example of the temperature rise curve. According to the present invention, the temperature of the pure water is raised as shown by the line A, and the water electrolysis is started when the temperature reaches, for example, 80 ° C. Therefore, a low electrolytic cell voltage can be maintained. However, in the conventional water electrolysis method, as shown by the line B, the water temperature is low at the start of water electrolysis, and the temperature of pure water increases through continuation of electrolysis, so that the electrolysis cell voltage increases.

As described above, the temperature of the pure water reaches the predetermined temperature (6
When the temperature reaches a predetermined temperature in the range of 0 to 120 ° C.), the power supply to the electric heater 14 is stopped. Next, electricity is supplied to the electrolytic cell 11 to start water electrolysis. During water electrolysis, the temperature of pure water gradually increases due to part of the electric energy for electrolysis,
In order to keep the temperature of the pure water substantially constant, cold water is appropriately introduced into the heat exchanger 15 and heat is indirectly exchanged with the pure water circulating in the circulation path 16.

With the temperature of the pure water to be subjected to water electrolysis maintained at a predetermined temperature in the range of 60 to 120 ° C.,
Water electrolysis is performed according to the above-described process, oxygen gas is discharged from the path 18, and hydrogen gas is discharged from the path 20, and can be used for various applications.

When the water electrolysis temperature is set to 80 ° C., in order to stabilize the generation amounts of hydrogen gas and oxygen gas, the heat exchanger 15 is controlled to maintain the electrolysis temperature at about 80 ± 3 ° C. It is preferable to control the exchange amount.
In addition, as electrolysis temperature, 80 degreeC is more preferable than 60 degreeC. This is because the current density can be increased at 80 ° C., so that the generation amounts of hydrogen and oxygen gas increase, and the generation efficiency of hydrogen and oxygen increases. On the other hand, when the electrolysis temperature is lower than 60 ° C., in order to prevent the elution of Ir and Ru and perform electrolysis, it is necessary to reduce the electrolysis current. .

FIG. 5 is an overall flow chart of another embodiment of the solid polymer electrolyte type water electrolysis apparatus of the present invention. FIG.
The electric heater 14 in FIG. 3 is replaced with a hot water inlet 27, and the temperature of pure water is raised by indirect heat exchange between hot water and pure water instead of the temperature rise of pure water by the electric heater 14. It is intended. After the temperature of the pure water is raised to a predetermined temperature in the range of 60 to 120 ° C. by the hot water flowing into the hot water inlet 27, the flow of the hot water is stopped, and the cold water is appropriately supplied to the heat exchanger 15. Pass through,
The temperature of the pure water circulating in the circulation path 16 can be kept constant. The water flowing into the hot water inlet 27 is not particularly limited, and, for example, general industrial water can be used. Heat can be used.

Next, the actual capacity of an electric heater or a hot water passing device when performing water electrolysis with a water electrolyzer as shown in FIG. 3 or FIG. 5 will be described.
In the case of m ³ / hr, the temperature of pure water is increased from 10 ° C to 80 ° C by 1
When the temperature is raised over time, an electric heater having a capacity of 4 kW may be used. In the case of a hot water inlet, the electrolysis temperature is 80 ° C.
In order to achieve this, a heat transfer area of about 0.3 m ² may be used, and hot water at about 100 ° C. may be passed at 1 ton / hr. Thus, it is not necessary to use a large-capacity electric heater, and the heat transfer area of the hot water inlet may be small. In addition, after raising the pure water to a predetermined temperature, electric energy or hot water as a heat source is not required, and the required energy is substantially only electric power for water electrolysis. Can be.

[0027]

According to the water electrolysis apparatus and the water electrolysis method of the present invention, it is possible to generate hydrogen and oxygen at a low voltage, and the electrolysis voltage is increased even if water electrolysis is performed at a high electrolysis current density. Never. Therefore, the running cost of water electrolysis can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a solid electrolyte membrane unit.

FIG. 2 is a diagram showing a time course of an electrolytic cell voltage when water electrolysis is performed at 80 ° C.

FIG. 3 is an overall flow chart of one embodiment of a solid polymer electrolyte type water electrolysis device of the present invention.

FIG. 4 is a diagram comparing a temperature rise curve of pure water in the water electrolysis method of the present invention and a temperature rise curve of pure water in the conventional water electrolysis method.

FIG. 5 is an overall flowchart of another embodiment of the solid polymer electrolyte water electrolysis device of the present invention.

FIG. 6 is a diagram showing a relationship between a current density and an electrolytic cell voltage.

FIG. 7 is a diagram showing a time course of an electrolytic cell voltage when water electrolysis is performed at 30 ° C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 ... Electrolysis cell 2 ... Solid electrolyte membrane 3 ... Porous feeder 4 ... Electrode plate 12 ... Electrolysis tank 13 ... Pump 14 ... Electric heater 15 ... Heat exchanger 16 ... Circulation path of pure water 27 ... Hot water passage vessel

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K021 AA01 BA02 BB05 BC05 CA05 CA08 CA09 CA10 CA11 CA12 CA15 DB12 DB18 DB31 DB43 DC01 DC03

Claims (7)

[Claims] 1. An electrolytic cell in which a metal or oxide is plated on both sides of a solid electrolyte membrane, porous feeders are arranged on both sides of the solid electrolyte membrane, and an electrode plate is arranged outside each of the porous feeders. In the solid electrolyte type water electrolysis apparatus comprising, the metal or oxide is a platinum group metal or an alloy thereof or an oxide thereof having an anode overvoltage lower than platinum, and provided with heating means for pure water for water electrolysis. Solid electrolyte type water electrolysis device. 2. The solid electrolyte type water electrolysis apparatus according to claim 1, wherein the platinum group metal is Ir or Ru. 3. The solid electrolyte type water electrolysis apparatus according to claim 1, wherein the solid electrolyte membrane is a solid polymer electrolyte membrane. 4. A platinum group metal having a lower anode overvoltage than platinum, an alloy thereof or an oxide thereof is plated on both surfaces of the solid electrolyte membrane, and a porous feeder is disposed on both sides of the solid electrolyte membrane. Using a solid electrolyte type water electrolysis device consisting of an electrolytic cell with an electrode plate arranged outside the power feeder,
A water electrolysis method comprising heating pure water to a high temperature in advance and then performing water electrolysis. 5. The water electrolysis method according to claim 4, wherein the platinum group metal is Ir or Ru. 6. The water electrolysis method according to claim 4, wherein the temperature of the water electrolysis is 60 to 120 ° C. 7. The water electrolysis method according to claim 4, wherein the solid electrolyte membrane is a solid polymer electrolyte membrane.