Water electrolysis method and apparatus

Abstract

A method and apparatus for alkaline electrolysis with hydrogen generation are disclosed herein. The system includes substantially identical first and second charged batteries 11a and 11b, each of which includes a zinc-plated first electrode 12a, 12b made of copper, silver, or an alloy thereof, a second electrode 13a, 13b containing an iron catalyst, an aqueous alkaline solution 14a, 14b immersing the first and second electrodes, and outlets 15a, 15b configured to allow gas generated at the second electrode to escape from the batteries 11a, 11b. A power supply element disposed between the first and second electrodes shorts the two batteries and has a specific polarity that ensures a voltage between the battery electrodes is greater than 1.3 V. In this configuration, the first battery performs a discharging process while producing hydrogen gas. Optionally, the second battery performs a charging process while producing oxygen gas. When the first battery's discharge cycle is completed, the polarity of the power supply is reversed so that the second battery discharges while producing hydrogen gas, while the first battery recharges while producing oxygen gas. This polarity reversal is repeated periodically so that oxygen and hydrogen are alternately produced in the two batteries.

Description

Technical Field

[0001] The present invention relates to a method of water electrolysis, and more particularly to a method of generating hydrogen by electrolysis.

[0002] The present invention also relates to a water electrolysis apparatus, and more particularly to an apparatus for generating hydrogen gas.

Background Art

[0003] Compared with hydrogen generation processes such as steam reforming and other hydrocarbon generation methods, it is known that there are significant limitations to hydrogen generation by water electrolysis on a commercial scale due to its low efficiency. However, from the perspective of environmental sustainability, research is underway to improve the efficiency of electrolysis systems, and the realization of commercial-scale hydrogen generation by electrolysis is desired.

[0004] An electrolysis apparatus comprises a plurality of electrochemical cells connected in series. An electrochemical cell consists of two half-elements, also called half-cells. These half-elements are separated by a semipermeable membrane. When appropriately connected via an external electrical circuit, electrons generated by an oxidation reaction occurring in one half-element migrate to the other half-element, causing a reduction reaction. Generally, a half-element consists of a metal electrode immersed in an electrolytic medium. In an electrolytic cell, the electrical energy required to carry out this process is supplied from an external electrical circuit connected to the electrodes of the cell. Therefore, electrolysis does not occur spontaneously, and the difference in Gibbs free energy in this process is greater than zero. Electrolysis follows Faraday's law, according to which, for an electrolysis reaction to occur, the minimum voltage between the electrodes of the cell of the electrolysis apparatus must be 1.23 V under standard temperature and pressure conditions (298 K, 1 bar). When the voltage value between the electrodes of the cell is lower than this under standard temperature and pressure conditions, water electrolysis occurs.

[0005] Among electrolysis processes, alkaline electrolysis is one of the most widely known, but its efficiency is low. In alkaline electrolysis, the electrolyzer comprises two electrodes immersed in an electrolyte of an alkaline aqueous solution containing 20% to 30% by weight of potassium hydroxide (KOH). These two electrodes are conventionally made of nickel-plated steel and are separated by a membrane (generally a positively charged polymer material). This ensures that the generated gases are also separated, from the perspectives of efficiency and safety. Furthermore, the membrane needs to be permeable to hydroxide anions and water molecules.

[0006] JPEG0007709754000001.jpg160150

[0007] Since 1980, research on solid oxide electrolysis cells (SOECs) has been pursued, and in this technical field, very high efficiencies exceeding 100% have been achieved through operation at high pressures and the use of catalysts made of non-noble metal materials. Furthermore, a more interesting feature of SOECs is that due to their chemical flexibility and operation at high temperatures, they can be applied to the electrolysis of carbon dioxide to carbon monoxide, as well as the electrolysis of carbon monoxide from H2O / CO2 to H2 / CO (syngas). Therefore, if the issues regarding the durability of ceramic materials during high-temperature and long-term operation are resolved, there is no doubt that this technology shows great potential for hydrogen production in the future.

[0008] The solid polymer electrolysis process has also been established. Different from alkaline electrolysis devices, polymer electrolyte membranes (PEMs) utilize solid electrolytes. Therefore, the membrane is a polymer ion exchange membrane. Here, those made of fully fluorinated polyethylene together with sulfonic acid groups such as "Nafion" and carboxylic acids such as "Flemion" are the most common. The membrane has high proton conductivity, low gas exchange, a compact system configuration, and a high operating pressure (up to 4 MPa). It can also exhibit high performance even at high temperatures between 80 degrees and 150 degrees. PEM electrolysis devices can operate at very high current values. In fact, that value is approximately 2 A / cm2 and this can reduce the operating cost, potentially reducing the overall cost of electrolysis. However, at present, PEM electrolyzers have high manufacturing costs and few merits for commercial-scale use.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The main object of the present invention is to propose a method for alkaline electrolysis with enhanced efficiency.

[0011] Another object of the present invention is to propose an alkaline electrolysis method that operates under standard temperature and pressure conditions and enables hydrogen generation by supplying a voltage of less than 1.23V.

[0012] A further object of the present invention is to propose an alkaline electrolysis apparatus with enhanced efficiency.

[0013] Another object of the present invention is to propose an alkaline electrolysis apparatus configured to operate under standard temperature and pressure conditions while being supplied with power at a voltage of less than 1.23V.

Means for Solving the Problems

[0014] According to one aspect of the present invention, the above-described object can be achieved by a water electrolysis apparatus. The apparatus is a first Battery which is copper, silver, or Copper and silverIt is a first electrode made of an alloy and plated with zinc, in which zinc migrates into the liquid as an alternative and deposits on the gas electrode following the redox reaction carried out in the cell. A second electrode having an iron catalyst that generates oxygen gas and hydrogen gas as alternatives following the redox reaction carried out in the cell. An aqueous alkaline solution that immerses the first electrode and the second electrode. An outlet formed according to the second electrode and configured to allow the gas generated at the second electrode to escape from the electrochemical cell. Having a first Battery And First Battery A second that is substantially the same as Battery And Connection means for short - circuiting the first electrode of the first battery electrically with the first electrode of the second battery by connecting the first electrodes to each other. Connection means for short - circuiting the second electrode of the first battery electrically with the second electrode of the second battery by connecting the second electrodes to each other. Connecting the first electrode The connection of A power supply member connected to the connecting means, which can supply only a voltage of less than 1.2V and has a specific polarity. Polarity reversal means configured to reverse the polarity of the power supply member. A control member configured to operate the polarity reversal means periodically. Comprising.

[0015] In the alkaline electrolysis device shown above, under standard temperature and pressure conditions, by supplying power having a voltage of less than 1.23V from the outside, hydrogen generation becomes possible.

[0016] Electrolysis in an alkaline environment allows for a significant reduction in the cell charging voltage compared to electrolysers in an acidic environment, which increases the efficiency in particular. Alkaline electrolysis offers further advantages: firstly, it reduces the cost of the catalyst compared to platinum group metal-based catalysts used in acidic environments; furthermore, due to the use of a replaceable electrolyte and the low solubility of the anode catalyst, alkaline electrolysis allows for a longer battery life; and finally, due to the low diffusivity of gases in alkaline electrolytes, the purity of the gas produced is high.

[0017] On the other hand, prior art alkaline batteries require anionic membranes that perform poorly when used in solid-state electrolysis compared to cationic "Nafion"-based membranes. Thus, in many cases, these membranes have technical challenges in not functioning in alkaline environments, despite the advantages mentioned above. The present invention overcomes these limitations by utilizing a dual half-cell system that does not require a membrane.

[0018] According to another aspect of the present invention, the above-mentioned object can be achieved by a water electrolysis method, comprising the steps of: Almost identical 1 V Battery and 2 V Each of them is Copper, silver, or Copper and silver a first electrode made of an alloy of a second electrode having an iron catalyst; an alkaline aqueous solution in which the first electrode and the second electrode are immersed; an outlet configured in response to the second electrode and configured to allow gas generated at the second electrode to escape from the battery; and both batteries have an inter-electrode voltage of 1.2V or less when fully charged, and the first battery is set in a fully charged state and the second battery is set in a fully discharged state. 1 V Battery and 2 V placing a battery; A power source interposed between a first electrode and a second electrode, which supplies a voltage of 1.2 V or less with a specific polarity to cause the voltage between the electrodes of both batteries to be higher than 1.3 V. Further, while the first battery starts discharging while generating hydrogen gas at the second catalyst electrode and discharging it from the discharge port, at the same time, the second battery starts charging while generating oxygen gas at the second electrode and discharging it from the discharge port. A step of short-circuiting the first battery and the second battery by a power source; When the first battery is in a discharged state and the second battery reaches a charged state, a step of reversing the polarity of the power source so that the second battery starts discharging while generating hydrogen gas at the second catalyst electrode and discharging it from the discharge port, and at the same time, the first battery starts charging while generating oxygen gas at the second electrode and discharging it from the discharge port; A step of periodically repeating the polarity reversal of the power source by selectively and alternately discharging oxygen and hydrogen from the second electrodes of the first battery and the second battery through their respective discharge ports; Comprising.

[0019] In the electrolysis method according to the present invention, by supplying an external voltage of less than 1.23 V, hydrogen can be generated. Therefore, depending on the situation, a pair of electrochemical cells, which are a battery and an electrolytic cell, add the voltage of the electrodes of the charged cell to an external generator, and a sufficient voltage is ensured for electrolysis.

[0020] These features and advantages of the present invention, as well as other features and advantages, will become more apparent by referring to the following drawings and checking the detailed description (not limited thereto) of the embodiments of the present invention. The drawings are as follows.

Brief Description of Drawings

[0021]

Figure 1

Figure 2

Best Mode for Carrying Out the Invention

[0022] Referring to FIGS. 1 and 2, reference numeral 10 indicates an electrolysis apparatus according to the present invention throughout. The apparatus 10 includes first battery 11a and second battery 11b which are substantially identical to each other. 1 V battery 11a and second 2 V battery 11b.

[0023] Referring to FIG. 1, both batteries 11a and 11b are schematically shown, and among other things, important elements of one of the electrochemical cells constituting the battery are emphasized. On the other hand, FIG. 2 shows an advantageous electrical connection arrangement between the electrodes of the corresponding electrochemical cell. One of the above-described electrochemical cells substantially consists of copper, silver, or an alloy thereof, and is zinc-plated, with first electrodes 12a, 12b, second electrodes 13a, 13b in which an iron catalyst is incorporated into a support made of a microporous material, and alkaline aqueous solutions 14a, 14b obtained by dissolving a certain amount, preferably 20 wt% to 30 wt% of potassium hydroxide (KOH) in water. Both batteries 11a, 11b also have discharge ports 15a, 15b. Through these discharge ports, the gases generated according to the second electrodes 13a, 13b of the corresponding electrochemical cells are discharged.

[0024] The first electrode 12a of the first battery 11a and the first electrode 12b of the second battery 11b are electrically short-circuited by the first connection means 16. On the other hand, the second electrode 13a of the first battery 11a and the second electrode 13b of the second battery 11b are electrically short-circuited by the second connection means 17. Here, the expression "electrically short-circuited" refers to a specific electrical connection that has an electrical resistance that can be ignored with respect to the resistance of the entire circuit. Such a state can be obtained by a cable made of copper alone or other materials having similar conductivity. Therefore, the two batteries 11a and 11b are electrically connected to each other in a short-circuited state in a closed circuit. Referring to FIG. 1, the DC power supply member 18 is connected to the second connection means 17 and supplies a voltage of less than 1.2 V between the second electrodes 13a and 13b having a specific polarity. Alternatively, as shown in FIG. 2, the power supply member 18 may be connected to the second connection means 16 or both connection means 16 and 17 (a modified example not shown). Thereby, the power supply member 18 can supply a voltage not exceeding 1.2 V. The current switch 19 is preferably connected to the second connection means 17 or the first connection means 16 and can selectively open and close the circuit between the two batteries 11a and 11b. The polarity reversing means 21 is connected to the power supply member 18 and is configured to reverse the polarity of the latter. Further, the control member 22 is considered and configured to periodically operate the polarity reversing means 21. Thereby, the voltage supplied from the power supply member 18 to the circuit is periodically reversed.

[0025] The method of operating the electrolysis device 10 described above is as follows. Referring to FIG. 1, the first battery 11a is arranged in a fully charged state and includes a first electrode 12a as a negative electrode and a second electrode 13a as an anode. The voltage between both electrodes is in the range of about 0.8V, at least 0.5V to 1.2V. The second battery 11b is in a discharged state. When the circuit is in a closed state by the current switching 19, the power supply member 18 is arranged with a polarity such that the corresponding negative electrode is connected to the second electrode 13a of the first battery 11a and the corresponding anode is connected to the second electrode 13b of the second battery 11b. Therefore, an additional voltage in the range of about 0.8V, at least 0.5V to 1.2V is supplied to the circuit. In such a state, the voltage at the ends of the first battery 11a and the second battery 11b is about 1.6V, at least exceeding 1.23V, and the chemical reactions occurring therein are not spontaneous, that is, there is no voltage higher than 1.23V at the electrode ends. In particular, the first battery 11a performs a discharging process and the second battery 11b performs a charging process. More specifically, in the first battery 11a during discharging, zinc covering the first electrode 12a migrates into the aqueous solution in the electrolyte to form potassium tetrahydroxozincate (Zn(OH)4K). On the other hand, at the second electrode 13a (catalyst), hydrogen gas (H2(g)) is released from the discharge port 15a. At the same time, in the second battery 11b during the charging process, zinc that has become potassium tetrahydroxozincate in the electrolyte is deposited as zinc metal on the first electrode 12b. On the other hand, at the second electrode 13b (catalyst), oxygen gas (O2(g)) is released from the discharge port 15b.

[0026] When the discharge cycle of the first battery 11a is completed, the charging cycle of the second battery 11b is also completed. Here, the control unit 22 operates the polarity reversing means 21, preferably by time control, to reverse the polarity of the power supply member 18. As a result, the second battery 11b starts a discharge cycle, and the first battery 11a starts a charging cycle. More specifically, in the second battery 11b during the discharging process, the zinc metal covering the first electrode 12b migrates into the aqueous solution in the electrolyte to form potassium tetrahydroxozincate (Zn(OH)4K). On the other hand, at the second electrode 13b (catalyst), hydrogen gas (H2(g)) is released from the discharge port 15b. At the same time, in the first battery 11a during the charging process, zinc that has become potassium tetrahydroxozincate precipitates on the first electrode 12a in the electrolyte. On the other hand, at the second electrode 13a (catalyst), oxygen gas (O2(g)) is released from the discharge port 15a.

[0027] Here, the electrolysis device 10 completes one cycle with the first battery 11a in the initial fully charged state and the second battery 11b in the initial discharged state. During the first half of the half cycle, the first battery 11a generates hydrogen, and the second battery 11b generates oxygen. Then, when polarity reversal occurs during the second half of the half cycle, the first battery 11a generates oxygen, and the second battery 11b generates hydrogen. In both batteries 11a and 11b, water consumption from the electrolyte occurs.

[0028] From a chemical perspective, zinc metal oxidizes in the batteries 11a and 11b during the discharging process. Zn(s)+4H2O=[Zn(OH)4] 2- +2H2↑-2e Zn(s)→Zn 2+ +2e On the other hand, during the charging process, the following reactions occur. [Zn(OH)4] 2+ +2e=Zn+2H2O+O2↑ Zn 2+ +4 e- →2Zn(s)

[0029] Since both hydrogen gas and oxygen gas are generated at the second electrodes 13a and 13b, they are discharged from the same discharge ports 15a and 15b during two consecutive half-cycles. It is advantageous in that a purge system can be appropriately provided that prevents the hydrogen gas and the oxygen gas from mixing within the structure, due to the structure for releasing the gas from the discharge ports.

[0030] From a structural point of view, in the alkaline electrolysis apparatus according to the present invention, the batteries 11a and 11b can have an electrochemical cell arranged in a monopolar or bipolar configuration. Further, since both hydrogen and oxygen are generated in response to the same electrodes (the second electrodes 13a and 13b), it is not necessary to provide a membrane having a function of separating the generated gases between the electrodes. However, a membrane can be provided for the purpose of preventing the gas from diffusing toward the first electrodes 12a and 12b. As the second electrode, by using a porous nickel support obtained by covering with a paste composed of iron and nickel powder and impregnating a porous support with a binder, preferably Teflon (registered trademark), the efficiency can be further increased, which is advantageous.

[0031] By the above-described electrolysis apparatus, a hydrogen generation method by electrolysis according to the present invention can be executed.

[0032] The method according to the present invention includes a step of installing an appropriate apparatus and a step of efficiently generating hydrogen by electrolysis by suppressing the input of external energy to the limit. More specifically, referring to FIG. 1 again, the method of the present invention includes preparing a first battery 11a and a first battery charged-type battery 11b that are substantially identical to each other. Each battery includes the following. · First electrodes 12a and 12b made of copper, silver, or an alloy thereof and zinc-plated · Second electrodes 13a and 13b having an iron catalyst · Alkaline aqueous solutions 14a and 14b in which the first electrode and the second electrode are immersed · Discharge ports 15a and 15b formed in response to the second electrodes 13a and 13b and configured to discharge the gas generated at the second electrodes from the battery

[0033] Both batteries 11a and 11b are configured to have a voltage in the range of about 0.8V, at least 0.5V to 1.2V, between the electrodes in a fully charged state. The first battery 11a is installed in a fully charged state, while the second battery 11b is installed in a fully discharged state.

[0034] The first battery 11a and the second battery 11b are electrically short-circuited between the first (or second) electrodes 12a and 12b by the power supply member 18. The above-mentioned power supply member 18 is configured to supply a voltage in the range of about 0.8V, at least 0.5V to 1.2V, with a specific polarity. By doing so, the voltage generated by the power supply member 18 can be added to the voltage between the electrodes of the first battery 11a in the fully charged state described above. Therefore, the voltage between the electrodes of the battery becomes higher than 1.3V. In this way, the first battery 11a performs a discharging process, generates hydrogen gas in the vicinity of the corresponding first 2 batteries electrode 13a, and discharges it from the corresponding discharge port 15a. Depending on the situation, the second battery 11b starts charging, generates oxygen gas in the vicinity of the corresponding second electrode 13b, and releases it from the corresponding discharge port 15b.

[0035] When the discharge of the first battery 11a and simultaneously the charging of the second battery 11b are completed, preferably, after a predetermined time has elapsed, the polarity of the power supply member 18 is reversed. As a result, the second battery 11b starts discharging, generates hydrogen gas at the corresponding second 2 batteries electrode 13b, and discharges it from the corresponding discharge port 15b. At the same time, the first battery 11a starts charging, generates oxygen gas at the corresponding second electrode 13a, and discharges it from the corresponding discharge port 15a.

[0036] When both the discharge of the second battery 11b and the recharge of the first battery 11a are completed, the polarity of the power supply member 18 is reversed again. By periodically repeating such polarity reversal, oxygen and hydrogen are selectively and alternately generated from the respective second electrodes 13a and 13b of the first battery 11a and the second battery 11b.

[0037] As can be easily understood, by the method described above, the electrolysis process for generating hydrogen and oxygen is realized by an extremely small external power supply with a required power supply of about 0.8 V in numerical value.

[0038] The advantages of the alkaline electrolysis apparatus for hydrogen generation and the method for generating hydrogen by alkaline hydrolysis according to the present invention, described in the above embodiments, do not change at all in modified examples or other embodiments. In the apparatus according to the present invention, the matters described here relate to general mechanisms and operating principles, and it should be surely understood that, in practical implementation, many forms will be taken to realize the described configurations and concepts. Therefore, the matters described and shown here are merely illustrative and do not limit the configurations and concepts. Accordingly, the electrolysis apparatus according to the present invention and the related method for alkaline electrolysis for hydrogen generation include further modified examples and practical modifications as long as they do not deviate from the scope of the appended claims.

Claims

1. A first battery comprising one or more electrochemical cells, wherein each electrochemical cell has a first electrode made of copper, silver, or an alloy of copper and silver, and plated with zinc, wherein the zinc migrates into the liquid and deposits on the gas electrode following the oxidation-reduction reaction occurring in the cell; a second electrode having an iron catalyst that alternately generates oxygen gas and hydrogen gas following the oxidation-reduction reaction occurring in the cell; an alkaline aqueous solution in which the first electrode and the second electrode are immersed; a first battery having at least one discharge port configured to release the gas generated corresponding to the second electrode of the corresponding electrochemical cell from the first battery; a second battery identical to the first battery; connection means for electrically short-circuiting the first electrode of the first battery with the first electrode of the second battery by connecting the first electrodes to each other; connection means for electrically short-circuiting the second electrode of the first battery with the second electrode of the second battery by connecting the second electrodes to each other; a DC power supply member connected to the connection means of the first electrode or the second electrode, capable of supplying only a voltage of less than 1.2 V and having a specific polarity; polarity reversal means configured to reverse the polarity of the power supply member; a control member configured to operate the polarity reversal means periodically; A water electrolysis device comprising the above, characterized in that.

2. The alkaline aqueous solution contains potassium hydroxide. The water electrolysis device according to claim 1, characterized in that.

3. The second electrode comprises a support made of a material impregnated with a binder together with a paste composed of iron powder and nickel powder. The water electrolysis device according to claim 1 or 2, characterized in that.

4. The first battery and the second battery are electric batteries configured to generate a voltage of less than 1.2 V between the corresponding electrodes in a fully charged state. The water electrolysis device according to claim 1 or 2, characterized in that.

5. A water electrolysis method for electrolyzing water using the water electrolysis device according to any one of claims 1 to 4, wherein The first battery and the second battery have an inter-electrode voltage of 1.2 V or less in a fully charged state, and the first battery is arranged in a fully charged state and the second battery is arranged in a fully discharged state, and a step of arranging the first battery and the second battery; A power source interposed between the first electrode and the second electrode, and further, the voltage between the electrodes of the first battery and the second battery is made higher than 1.3 V. At the same time, the second battery starts charging while generating oxygen gas at the second electrode and discharging it from the discharge port. A step of short-circuiting the first battery and the second battery with a power source that supplies a voltage of 1.2 V or less with a specific polarity; When the first battery becomes discharged and the second battery reaches a charged state, the second battery starts discharging while generating hydrogen gas at the second electrode and discharging it from the discharge port. At the same time, a step of reversing the polarity of the power source so that the first battery starts charging while generating oxygen gas at the second electrode and discharging it from the discharge port; A step of periodically repeating the polarity reversal of the power source by selectively and alternately discharging oxygen and hydrogen from the second electrodes of the first battery and the second battery through the respective discharge ports; A method for water electrolysis, characterized by the above.

6. The method for water electrolysis according to claim 5, further comprising a purge step of purging from the discharge port between the step of extracting oxygen and the step of extracting hydrogen from each of the second electrodes.

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