Hydrogen production and chemical energy storage

Abstract

Two-stage hydrogen production involves an electrolytic cell containing a first electrode and a second electrode and a solution comprising a metal salt. The first electrode and the second electrode are connected to an external electrical energy source during the charging phase, which causes the metal of the metal salt to be deposited on the first electrode and oxygen to be released on the second electrode. After the charging phase is completed, the first electrode and the second electrode are disconnected from the external electrical energy source, and the electrolytic cell containing the deposited metal is kept in a standby state until hydrogen needs to be produced. During the discharge phase, the first electrode and the second electrode are short-circuited such that metal is dissolved from the first electrode and hydrogen is released from the second electrode without any significant simultaneous extraction of electrical energy. The production of hydrogen is thus correspondingly increased. The invention further provides the variant.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. patent application No. 17 / 742,125, filed on May 11, 2022, the entire contents of which are incorporated herein.

[0003] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0004] not applicable. Technical Field

[0005] The present invention relates to hydrogen production and chemical energy storage. In particular, it relates to methods, systems and devices for producing and storing hydrogen, thereby providing energy storage in the form of increased hydrogen potential energy. Background Art

[0006] The electrolysis of water into hydrogen and oxygen is a long-standing process. As the renewable energy mandate continues to be pursued, a significant obstacle has been the relatively low availability and reliability associated with renewable energy sources. For example, for solar energy, its availability is limited by the amount of sunshine in a particular region or in a particular season or under particular weather patterns. Similarly, for wind energy, the conditions for generating energy from a wind source must also be at least adequate, if not optimal, in terms of wind activity at a particular location and at a particular time. Ideally, the ability to "meet demand" also means being able to change and introduce more of such energy as needed, independent of current conditions. Therefore, changing energy storage and meeting the demand for utilizing such renewable energy sources becomes important for the long-term viability of renewable energy sources at levels sufficient to achieve targeted renewable energy generation targets and reduce carbon emissions associated with public policies.

[0007] Energy storage for renewable electricity remains a challenge for larger scale operations that need to accommodate significant electrical loads and / or extended time periods.

[0008] Effective systems for enhanced hydrogen production associated with renewable and other power generation that provide energy storage in the form of hydrogen potential energy until there is a demand for electrical energy are currently very limited, but are greatly needed. Summary of the invention

[0009] The present disclosure relates to methods and systems for enhancing electrochemical production of hydrogen to serve as a useful renewable energy source. Such systems and methods provide the ability to increase the storage of energy as hydrogen potential energy until there is an electrical energy demand that needs to be met. The present disclosure provides the use of electrochemical reactions to produce hydrogen in a particularly adapted environment. In an embodiment of the present disclosure, a method and system for hydrogen production are provided, wherein two operating stages are adopted. The system includes an electrolytic cell containing a first electrode and a second electrode and a solution. The solution can be an acidic or alkaline aqueous solution and can contain salts of various metals, provided that each of these metals can be dissolved by releasing hydrogen as an electronic balance reaction. Therefore, the present invention can be operated with a solution containing metal cations (such as iron, nickel, manganese, zinc, tin and lead). However, the applicant has found that when the metal salt solution is a zinc-based salt solution, a better system efficiency can be obtained. Therefore, for simplicity, in the following part of this document, only zinc solutions will be mentioned, but the above-mentioned other metals can also be used. The first electrode may be made of a metal or metal alloy (e.g., zinc, copper, stainless steel, or titanium), and the second electrode may be made of one or more of stainless steel, nickel and its alloys, titanium and its alloys, or a graphitized carbon sheet or graphitized carbon paper, wherein the graphitized carbon sheet or graphitized carbon paper is optionally provided with a catalytic coating, wherein the catalytic coating is suitable for reducing the overvoltage of the oxygen evolution reaction (hereinafter referred to as "OER"), the hydrogen evolution reaction (hereinafter referred to as "HER"), or both. During the charging phase of the battery containing the zinc salt solution (see Figure 1 ) The first electrode and the second electrode are connected to an external electrical energy source, which may be a renewable energy source, such as solar or wind energy. The electron flow supported by the external power source is delivered to the first electrode, where the zinc of the zinc salt is reduced. The electrons delivered to the first electrode leave the second electrode, where oxygen is released by electrooxidation of water. After the charging phase is completed, the first electrode and the second electrode are disconnected from the external energy source (see Figure 2). In this standby state, the applicant has found that the zinc remains essentially stable because its surface is characterized by a high reduction potential relative to the standard hydrogen electrode (SHE), which prevents any significant oxidation of the metallic zinc. When hydrogen is required, that is, during the discharge phase of operation, the known prior art teaches connecting the first electrode and the second electrode to an external resistive circuit that allows electrons to flow from the first electrode (at which the zinc is subsequently dissolved by oxidation) to the second electrode, on the surface of which the electrons produce hydrogen by electroreduction of water. The release of hydrogen at the second electrode is facilitated by a reduced HER overvoltage, which, as already indicated, is characterized by the material used to construct the second electrode. This electrical layout accelerates the release of hydrogen, while electrical energy is simultaneously extracted from the cell through the external resistive circuit to perform work or to be stored. However, the applicant has found that the rate of release of hydrogen allowed by this known prior art layout is too low to be compatible with the type of large-scale applications for which the present invention is intended. Surprisingly, the applicant has found that when the external electronic circuit is short-circuited (see Figure 3 ), this serious obstacle can be overcome. The short circuit does not allow the extraction of electrical energy through an external resistive circuit as in the prior art layout, or at least reduces the residual electrical energy released in the second stage to less than 1% of the available energy for the zinc-hydrogen reaction. However, the applicant has found that the loss of this externally utilized electrical energy is more than compensated by the increased hydrogen release rate, which allows a significant reduction in the electrode area required to produce the amount of hydrogen that should be supplied to any large-scale application. In turn, the smaller electrode area leads to a significant reduction in the required capital investment. The applicant has also found that the hydrogen release rate can be further increased by maintaining the electrode gap in the range of 1.75-3.25 mm, preferably in the range of 2-3 mm, and maintaining the concentration of metallic zinc at 90-110 g / l, preferably 95-105 g / l, and more preferably 100 g / l.

[0010] In another embodiment of the present disclosure (see Figure 4 , 5 and 6), a system and method for hydrogen production are provided, in which two stages are employed. The system includes an electrolytic cell containing a first electrode and a second electrode, the first electrode comprising a metal selected from the group consisting of zinc, copper, stainless steel or titanium, and the second electrode being divided into two units electrically insulated from each other. The first unit of the second electrode may include titanium metal having a coating suitable for oxygen release. The second unit of the second electrode may include nickel, nickel alloy, stainless steel or graphitized carbon material (such as carbon sheet or carbon paper), all of which have an optional coating for promoting hydrogen release. The battery includes a solution containing a zinc salt. During the charging stage (see Figure 4) The first cell of the first electrode and the second electrode are connected to an external electrical energy source. Zinc metal is deposited on the first electrode and oxygen is released on the first cell of the second electrode, characterized by a low OER overvoltage. After the charging phase is completed, the first cell of the first electrode and the second electrode are disconnected from the external energy source. In the following standby state (see Figure 5 ) Applicants have found that zinc is essentially stable due to the low rate of the coupled reaction for hydrogen evolution and is in fact characterized by a very high overvoltage on the zinc surface. When it is desired to release hydrogen at a given rate, i.e. during the discharge phase of operation (see Figure 6 ), the first electrode and the second cell of the second electrode are connected to an external short circuit, so that the zinc dissolves while hydrogen is released on the surface of the second cell of the second electrode, characterized by a reduced HER overvoltage. The external short circuit allows a hydrogen release rate compatible with large-scale applications, which is the object of the present invention, with all the advantages of reducing the electrode surface and reducing capital investment requirements as described above.

[0011] In another embodiment of the present disclosure, a system and method for hydrogen production are provided (see Figure 7 , 8 and 9). Two phases are used. The system includes an electrolytic cell provided with a first electrode and a second electrode and filled with a solution containing a zinc salt. The system also includes a connection to an external electrical energy source having a negative terminal and a positive terminal. During the charging phase (see Figure 7 ), the first electrode and the second electrode are connected to the negative terminal and the positive terminal of the external electrical energy source, respectively. During the charging phase, zinc is deposited on the first electrode and oxygen is released on the second electrode. After the charging phase is completed, the first electrode and the second electrode are disconnected from the external energy source, and the battery remains in a standby state until hydrogen production is required (see Figure 8 When hydrogen is needed, i.e., in the discharge phase, the first electrode and the second electrode are connected to opposite ends of the external energy source, i.e., the first electrode with the zinc deposit is connected to the positive terminal and the second electrode is connected to the negative terminal (see Fig. 9 The rate at which zinc dissolves from the first electrode and hydrogen is released at the second electrode can be controlled by controlling the voltage applied in the external circuit so that the voltage across the cell measured from the first electrode to the second electrode can be raised to a value even higher than that permitted by a simple short-circuit operation.

[0012] In another embodiment of the present disclosure, a system and method for hydrogen production is provided. In this embodiment, the applicant has found that if, in addition to each step in the above process, the electrolyte solution is heated during the discharge phase (see Fig.10), the hydrogen production rate can be further increased. Applicants have determined that heating of the solution can come from a number of available sources, such as resistive heaters, waste streams, or low demand steam sources (e.g., heat recovery steam generators (HRSGs)). Notably, sources that allow for affirmative (and alternating) heating and cooling of the solution (e.g., heat exchanger coils immersed in the solution, resistive heaters, induction heaters, or water jackets) may be ideal for this aspect of the disclosure.

[0013] Furthermore, the rate of hydrogen release in the short-circuit electrode arrangement of the present invention is affected or hindered by the electrode distance and the internal resistivity of the solution. It is highly preferred that the electrode distance is reduced to 1.75-3.25 mm, preferably 2-3 mm, ensuring the minimum distance required to prevent or limit the possibility of premature electrode shorting due to the known problem of zinc dendrites forming from the first electrode and contacting the second electrode. In addition to using high zinc salt concentrations as previously described, the internal resistivity of the solution can be significantly reduced by increasing the temperature of the cell. In fact, applicants have found that increasing the cell temperature to above 35-55°C, preferably 37.5-52.5°C; more preferably from the typical 40-50°C range of the charging stage to 75-105°C; preferably 77.5-102.5°C; more preferably, in the discharge stage, the range of 80-100°C can significantly increase the hydrogen release rate, thereby further resulting in a reduction in the required electrode surface area and the associated capital investment. Applicants have also found that after the discharge stage has been completed, the cell temperature should preferably return to the lower temperature level used in the charging stage to deposit zinc metal with optimal efficiency. Heating the solution will cause a slight loss in charging efficiency. However, it is preferred to minimize this loss by applying a heat exchange arrangement.

[0014] These and other features of the present disclosure will be discussed in greater detail in the description that follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of an embodiment of a charging phase of a method for hydrogen production is disclosed, which includes the use of an external power source, a battery comprising a first electrode and a second electrode connected to the external power source, and a solution comprising a zinc salt (which facilitates deposition of zinc metal on the first electrode and enables release of oxygen at the second electrode).

[0016] Figure 2 Public Figure 1 Schematic diagram of an embodiment After the charging phase has been completed, the first electrode and the second electrode are disconnected from the external power source and the cell containing the deposited zinc metal remains in a standby state until hydrogen production is required.

[0017] Figure 3 Publicly available including Figure 1 and Figure 2 Schematic diagram of an embodiment of a discharge phase of a method of hydrogen production in which a first electrode and a second electrode are short-circuited such that zinc metal oxidatively dissolves from the first electrode and releases hydrogen at an increased rate at the second electrode without significant generation of electrical energy.

[0018] Figure 4 , 5 and 6 disclose schematic diagrams of alternative embodiments of an electrolytic cell according to the present disclosure, wherein the second electrode comprises a first unit and a second unit that are electrically insulated from each other.

[0019] Figure 7 , 8 and 9 disclose schematic diagrams of alternative embodiments of the discharge phase of a method for producing hydrogen. The alternative embodiment comprises reversing the discharge phase according to Figure 1 The method of embodiments employs a polarity step during the charging phase. Figure 7 The charging phase in this alternative embodiment is shown, Figure 8 shows the standby state in this alternative embodiment, and Fig. 9 The discharge phase in this alternative embodiment is shown.

[0020] Fig.10 A schematic diagram of another alternative embodiment of the discharge phase of the method for hydrogen production is disclosed, which includes heating a solution of a zinc metal salt to 80-100° C. in addition to short-circuiting the first electrode and the second electrode.

[0021] Corresponding reference numerals are used for corresponding parts etc. as described in the specification and drawings. DETAILED DESCRIPTION

[0022] The following detailed description illustrates the claimed disclosure by way of example and not limitation. This description illustrates and enables those skilled in the art to make and use the claimed disclosure, and describes multiple embodiments, modifications, variations, substitutions, and uses of the claimed disclosure. In addition, it should be understood that the claimed disclosure is not limited in its application to the details of the systems, methods, and devices specifically set forth in the description below or illustrated with the aid of the accompanying drawings. The claimed disclosure can have other embodiments and can be practiced or executed in various ways. In addition, it should be understood that the wording and terminology used herein are for descriptive purposes and should not be considered restrictive.

[0023] As used herein, the term "cell" refers to a container comprising: a first electrode, a second electrode, and optionally further electrodes, the second electrode being optionally divided into a first electrically insulating unit and a second electrically insulating unit; and a solution, preferably an aqueous solution, containing a dissolved metal salt, preferably a zinc salt, and optionally other dissolved chemicals, such as additives suitable for promoting metal deposition and preventing dendrite growth.

[0024] As used herein, the term "electrode" refers to a conductor through which electrons (electricity) enter or leave to participate in reactions on the electrode surface with chemical species present in solution contained within the battery. For example, in the charging phase of the present disclosure, the electrons flowing into the first electrode are generated by an external electrical energy source. At the interface between the first electrode surface and the solution, a reduction reaction occurs in which the electrons combine with zinc ions present in the solution, resulting in the deposition of zinc: Zn 2+ +2 electrons → Zn. The external energy source, which works as an electron pump, takes electrons from the second electrode, which are generated by the oxidation reaction occurring at the interface between the second electrode and the solution. This reaction manifests itself as OH contained in the solution. - Ions are converted into oxygen (O2) and water: 2OH – →0.5O2+H2O+2 electrons, when the solution is alkaline; or through the conversion of water in the aqueous solution into oxygen (O2) and H + :H2O→0.5O2+2H + +2 electrons when the solution is acidic.

[0025] As used herein, the term "catalyst" refers to any compound capable of promoting a given reaction. The term catalysis as used herein refers to the ability of the second electrode surface to promote oxygen evolution reaction, hydrogen evolution reaction or both, which in electrochemical terms refers to the ability to reduce the overvoltage of the reaction.

[0026] As used herein, the term "large-scale hydrogen production" or "large-scale chemical storage resources" refers to the amount of hydrogen or hydrogen potential energy required to support the operation of an electric power system in the range of many kW power, preferably in the range of at least 1 MW power.

[0027] Applicants have designed and disclosed a two-stage method, system and device herein that greatly improves the production of hydrogen and enables it to be used as a chemical energy storage resource for large-scale renewable energy operations. In addition, the increased capacity for storing this hydrogen energy potential greatly improves the ability to tap this energy potential in a timely manner when it is most needed. The present disclosure uses metal deposition / dissolution reactions, especially zinc deposition / dissolution reactions, and oxygen / hydrogen evolution reactions in a specially adapted environment (the environment is designed to increase the production rate of hydrogen using a two-phase system) to produce hydrogen. Generally speaking, during the charging phase, an external electrical energy source is connected to a first electrode and a second electrode of a battery containing a zinc salt solution. Specifically, the first electrode is connected to the negative polarity of the external power source and the second electrode is connected to the positive polarity, thereby establishing a voltage difference potential across the battery. The voltage difference allows current to flow through the battery, and the greater the current, the higher the voltage difference, resulting in the deposition of zinc metal contained in the solution on the first electrode in the form of a zinc salt, and the release of oxygen on the second electrode. After the charging phase is completed, the first electrode and the second electrode are disconnected from the external energy source, and the battery remains in this standby state until hydrogen production is required. The time that the battery remains in standby mode can vary significantly from almost instantaneous to considerable durations, such as 12 hours, or even days, weeks or longer. There are no practical limitations other than the need to consume the stored hydrogen and economic considerations on the scale of the hydrogen storage device. In the discharge phase, when hydrogen production is required, the zinc metal is oxidized and dissolved back into solution from the first electrode, and hydrogen is produced at the second electrode by short-circuiting the first electrode and the second electrode, without extracting any or only a small amount of electrical energy from the system, which is contrary to what is disclosed in the known prior art. Applicants have surprisingly discovered that the rate of hydrogen production can be significantly increased by directing all of the available potential energy of the battery constituted by the zinc dissolution reaction to the hydrogen evolution reaction, with the first electrode and the second electrode short-circuited. As an example, applicants have been able to produce hydrogen at 400m 3 / (hour×m 2 The rate at which hydrogen is released is calculated from the electrode surface, which allows one to satisfy the requirement of 350 m 2 The hourly hydrogen production requirement of a 1 MW power plant with limited electrode surface. The range of overvoltages that need to be applied to the electrode system during the charging phase within the parameters of the present disclosure in order to produce a reduced metal deposit on the first electrode and release oxygen on the second electrode is known to those skilled in the art without undue experimentation.

[0028] The first electrode and the second electrode of the cell may have a gap of 1.75-4.25, preferably 2-3, and in the preferred case of zinc metal, the solution may contain 50-70 g / L, preferably 55-65 g / L, and more preferably 60 g / L of metal cations. The applicant has also surprisingly found that it is particularly advantageous to combine the short-circuiting operation with increasing the concentration of zinc metal salt in the solution (e.g., up to 100 g / L of zinc cations) to reduce resistivity, improve material transport and reduce the electrode gap (e.g., a gap as low as 2-3 mm), which still allows reasonable trouble-free operation without any risk of internal short circuits between the first electrode and the second electrode due to metal dendrite growth. This combination results in the production of hydrogen at a higher rate than a simple short circuit. As an example, by using a layout including a short circuit, a high metal salt concentration and a reduced electrode gap, the applicant has found that the hydrogen production rate can be increased to about 550 m 3 / (hour×m 2 electrode surface), which corresponds to a surface area of ​​about 280 m 2 The hydrogen production required per hour for a 1 MW power plant with limited electrode surface. As further disclosed below, applicants have developed additional mechanisms to increase the production of hydrogen through various substitutions and combinations of the disclosed two-stage hydrogen production subject matter. Thus, applicants have provided greatly increased hydrogen potential for use as a chemical storage resource. In all two-stage systems disclosed herein, the system can be configured so that the battery of the system is connected to a separate external power source, or the system can be configured so that the external power source is folded into it as an integral part of the system.

[0029] Reference Figure 1 , 2 In the first embodiment of the present disclosure, a hydrogen production system 100 is provided. As described above, two operation phases are adopted, one for the charging phase (see Figure 1 ), a standby state that separates the charging and discharging phases (see Figure 2 ), and discharge phase (see Figure 3 ). System 100 includes an electrolytic cell 200 including a first electrode 10 and a second electrode 20. Electrolytic cell 200 is filled with a solution 30 containing a zinc salt 40. During the charging phase of operation (see Figure 1 ) The first electrode 10 and the second electrode 20 are connected to an external electrical energy source 300. During this charging phase, zinc metal 50 is deposited on the first electrode 10 and oxygen 60 is released on the second electrode 20. After the charging phase is completed, the first electrode 10 and the second electrode 20 are disconnected from the external energy source 300, and the charged battery containing the deposited zinc metal remains in a standby state until hydrogen production is required (see Figure 2 ). Once hydrogen is required, i.e. during the discharge phase of operation (see Figure 3), the first electrode 10 and the second electrode 20 are short-circuited, so that the zinc metal 50 is dissolved from the first electrode 10 to regenerate the metal salt back into the solution, and the hydrogen gas 70 is released at the second electrode 20. Therefore, referring to Figure 3 , the discharge phase of operation includes short-circuiting the first electrode 10 and the second electrode 20 .

[0030] The solution 30 in the electrolytic cell 200 may be alkaline or acidic. When the solution is alkaline, the zinc metal salt 40 comprises zinc as a complex, such as but not limited to zincate ZnO2 2- or zinc hydroxy complex Zn(OH)4 2- , and when the solution is acidic, the zinc salt can be zinc sulfate. The use of acidic or alkaline solutions is not a secondary issue. When an acidic solution is used with zinc sulfate as a zinc salt, this may result in partially loose zinc deposition and easier dendrite growth, which may reduce system efficiency and cause the risk of internal short circuits between the first electrode and the second electrode. In alkaline solutions, the metal deposition is denser and less prone to dendrite growth, both of which allow operation with a reduced electrode gap and ensure better efficiency. Alkaline solutions are also used to stabilize the system, making it practical to consider the use of a single second electrode (see the discussion below of alternative embodiments of using a second electrode divided into two electrically insulated first and second units). In fact, when the solution used is alkaline, the second electrode is preferably made of pure nickel or a nickel alloy. These materials are suitable for operation in the charging phase (where oxygen is released at a lower overvoltage) and the discharging phase (where hydrogen is also released at a lower overvoltage). In addition, these materials are characterized by having appropriate chemical stability to corrosive attack. In the embodiment using an alkaline solution, when the second electrode is made of high surface area nickel (such as sandblasted nickel or thermal sprayed nickel), it is particularly effective in further reducing the overvoltage, and minimal corrosion can also be expected.

[0031] When the solution is acidic, in addition to the loose deposition and dendrite growth effects already discussed, the poor performance of the second electrode can seriously affect the operation. In fact, it is only possible to obtain resistance to corrosive erosion during the charging phase when oxygen is released if the second electrode is made of titanium or a titanium alloy provided with a catalytic coating as taught by the prior art. However, such a second electrode is inoperable during the discharge phase when hydrogen is released. In fact, titanium becomes brittle and unsuitable for safe hydrogen production in acidic solutions due to the penetration of hydrogen into the metal lattice. Stainless steel, nickel and nickel alloys are suitable for use in the second electrode during the discharge phase when hydrogen is released, but are severely corroded during the charging phase when oxygen is released. The applicant has found that this negative feature can be overcome by adopting a second electrode divided into two electrically insulating units, as described below.

[0032] Reference Figure 4 , 5and 6, depicting an alternative two-stage system and method embodiment of hydrogen release 100. In this alternative embodiment, as Figure 1 , 2 In the embodiment shown in Figures 1 and 3, the electrolytic cell 200 contains two electrodes 10, 20. Preferably, the first electrode is made of zinc, copper, stainless steel or titanium. In an alternative embodiment of the hydrogen release system disclosed above, the second electrode 20 is divided into two units 20a, 20b, which are electrically insulated from each other. The first unit 20a of the second electrode 20 is preferably titanium metal, which has a coating suitable for oxygen release. Such coatings include precious metals and precious metal oxides, especially mixed iridium oxides and tantalum oxides disclosed in the patent literature. The second unit of the second electrode is preferably made of stainless steel, nickel and nickel alloys and graphitized carbon sheets or graphitized carbon paper, and it is preferably provided with a coating suitable for hydrogen release. Such coatings contain precious metals, such as ruthenium metal and platinum metal. The battery 200 includes a solution containing a zinc salt, especially an acidic solution, in which the use of a second electrode of a single structure is characterized by serious operating problems as previously expected. During the charging phase (see Figure 4 ) The first electrode 10 and the first cell 20a of the second electrode 20 are connected to an external electrical energy source 300. In this phase, zinc metal 50 is deposited on the first electrode 10 and oxygen 60 is released on the first cell 20a of the second electrode 20. After the charging phase has been completed, the first electrode 10 and the first cell 20a of the second electrode 20 are disconnected from the external electrical energy source 300 and the battery 200 remains in a standby state until hydrogen production is required, i.e. until the discharge phase begins (see Figure 5 ). In the discharge phase (see Figure 6 ), the first electrode 10 and the second cell 20b of the second electrode 20 are short-circuited, so that the second cell 20b of the second electrode 20 releases hydrogen 70 at a high rate, while the zinc metal 50 dissolves from the first electrode 10. Therefore, in this alternative embodiment, the first cell 20a of the second electrode 20 remains disconnected during the discharge phase. In addition to the advantage of releasing hydrogen at a high rate, this alternative embodiment has the advantages of less wear and longer service life of the second electrode unit. When a single second electrode 20 is used, oxygen production and hydrogen production occur on the same electrode, resulting in high cyclic voltage fluctuations, which leads to accelerated corrosion. In addition, this layout avoids hydrogen production on titanium electrodes, noting that titanium electrodes become brittle when hydrogen is produced in an acidic environment. Cell 20a is used only for oxygen production, and cell 20b is used only for hydrogen production, and the service life of these two cells is significantly extended.

[0033] Another alternative embodiment of the present disclosure is also directed to a two-stage system and method for enhancing hydrogen production. Figure 7 , 89, the system 100 includes an electrolytic cell 200, which contains a first electrode 10 and a second electrode 20 and is filled with a solution 30 containing a zinc salt 40. The system also includes an external electrical energy source 300 containing a negative terminal 300a and a positive terminal 300b. During the charging stage, the first electrode 10 and the second electrode 20 are connected to the negative terminal 300a and the positive terminal 300b of the external electrical energy source 300, respectively. During the charging stage, zinc deposits metal 50 on the first electrode 10 and releases oxygen 60 on the second electrode 20. After the charging stage is completed, the first electrode 10 and the second electrode 20 are disconnected from the external power source 300, and the battery remains in a standby state until hydrogen production is required, and hydrogen production occurs during the discharge stage. During the discharge stage, the first electrode 10 and the second electrode 20 are connected to the opposite ends of the external energy source 300, that is, the first electrode 10 is connected to the positive terminal 300b of the external energy source 300, and the second electrode 20 is connected to the negative terminal 300a of the external energy source 300. Zinc metal 50 dissolves from the first electrode 10 and releases hydrogen 70 at the second electrode 20. The hydrogen production rate is relative to Figure 1 , 2 The typical rate under simple short circuit conditions is greatly increased over the embodiment shown in Figure 3, even though this advantage is partially reduced by some additional power consumption. In addition, hydrogen production can be controlled by controlling the voltage of the external energy source 300 during the discharge phase.

[0034] In another embodiment, hydrogen release can be significantly increased by heating the solution during the discharge phase, since the elevated solution temperature can greatly reduce the internal resistance of the solution and the overvoltage on the second electrode for hydrogen production (see Fig.10 ). Applicants have found that increasing the cell temperature above the initial 35-55°C, preferably 37.5-52.5°C; more preferably the 40-50°C range during the charging phase to 75-105°C; preferably 77.5-102.5°C; more preferably the 80-100°C range during the discharge phase, can significantly increase the hydrogen release rate. This in turn leads to a further reduction in the required electrode surface area and the associated capital investment. Applicants have also found that after the discharge phase has been completed, the cell temperature should preferably be returned to the lower temperature level used in the charging phase to deposit zinc metal with optimal efficiency. Heating to, for example, the preferred 80-100°C range during the discharge phase significantly increases the hydrogen release rate, which in turn leads to a further reduction in the required electrode surface and the associated capital investment. After the discharge phase has been completed, the cell temperature should be returned to the temperature level used in the charging phase, for example 40-50°C, to deposit zinc metal with optimal efficiency. As previously mentioned, heating the solution will result in a small loss of efficiency, but this loss can be minimized if a heat exchange device is applied between the cells.

[0035] In summary, it can be seen that the various objects and advantages of the present disclosure have been achieved and other advantageous results obtained.

[0036] As various changes could be made in the above constructions without departing from the scope of the present disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A two-stage system for producing hydrogen, the system comprising an electrolytic cell, the electrolytic cell comprising a first electrode and a second electrode and a solution comprising a metal salt, and further, wherein the first electrode and the second electrode are configured to be connected to an external electrical energy source, so that during a charging phase, a metal of the metal salt is deposited on the first electrode and oxygen is released on the second electrode, and after the charging phase is completed, the first electrode and the second electrode are configured to be disconnected from the external energy source, and the cell containing the metal deposited on the first electrode is configured to remain in a standby state, and during a discharging phase, the first electrode and the second electrode are configured to be short-circuited, so that the metal dissolves from the first electrode and hydrogen is released on the second electrode.

2. The two-stage system of claim 1, wherein the solution is an alkaline solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

3. The two-stage system according to claim 2, wherein the zinc salt is selected from the group consisting of salts of zincates or zinc hydroxy complexes.

4. The two-stage system of claim 2, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, or titanium, and the second electrode comprises stainless steel, nickel, and a nickel alloy.

5. A two-stage system for producing hydrogen, the system comprising an electrolytic cell, the electrolytic cell comprising a first electrode and a second electrode and a solution comprising a metal salt, wherein the second electrode is divided into a first unit and a second unit electrically insulated from each other, wherein the first electrode and the first unit of the second electrode are configured to be connected to an external electrical energy source during a charging phase, so that a metal of the metal salt is deposited on the first electrode and oxygen is released from the first unit of the second electrode, the first electrode and the first unit of the second electrode are further configured to be disconnected from the external electrical energy source after the charging phase is completed, the cell containing the metal deposited on the first unit of the second electrode is configured to remain in a standby state, and the first electrode and the second unit of the second electrode are further configured to be short-circuited during a discharging phase, so that the deposited metal is dissolved from the first electrode and hydrogen is released from the second unit of the second electrode.

6. The two-stage system of claim 5, wherein the solution is an alkaline solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

7. The two-stage system according to claim 6, wherein the zinc salt is selected from the group of salts comprising zincates or zinc hydroxy complexes.

8. The two-stage system of claim 6, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, or titanium, and the second electrode comprises stainless steel, nickel, and a nickel alloy.

9. The two-stage system of claim 5, wherein the solution is an acidic solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

10. The two-stage system of claim 9, wherein the zinc salt is zinc sulfate.

11. The two-stage system of claim 9, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel and titanium, and the first unit of the second electrode comprises titanium metal and optionally further comprises a coating suitable for oxygen release, and wherein the second unit of the second electrode comprises stainless steel, nickel and nickel alloys and graphitized carbon sheets or graphitized carbon paper and optionally further comprises a coating suitable for hydrogen release.

12. A two-stage system for producing hydrogen, the system comprising an electrolytic cell, the electrolytic cell comprising a first electrode and a second electrode and a solution comprising a metal salt, the system being configured to be connected to an external electrical energy source having a negative polarity and a positive polarity, wherein the first electrode and the second electrode are configured to be connected to the negative terminal and the positive terminal of the external electrical energy source, respectively, so that during a charging phase, a metal of the metal salt is deposited on the first electrode and oxygen is released on the second electrode, and after the charging phase is completed, the first electrode and the second electrode are configured to be disconnected from the external energy source, the cell containing the metal deposited on the first electrode is configured to remain in a standby state, and during a discharging phase, the first electrode and the second electrode are configured to be connected to the positive terminal and the negative terminal of the external electrical energy source, respectively, so that the metal is dissolved from the first electrode and hydrogen is released on the second electrode.

13. The two-stage system of claim 12, wherein the solution is an alkaline solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

14. The two-stage system according to claim 13, wherein the zinc salt is selected from the group of salts comprising zincates or zinc hydroxy complexes.

15. The two-stage system of claim 13, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, or titanium, and the second electrode comprises stainless steel, nickel, or a nickel alloy.

16. A two-stage system for producing hydrogen, the system comprising: an electrolytic cell comprising a first electrode and a second electrode, the second electrode being divided into a first unit and a second unit electrically insulated from each other; a solution comprising a metal salt; and an external electrical energy source having negative and positive polarities, wherein the first cells of the first electrode and the second electrode are configured to be connected to the negative terminal and the positive terminal of the external electrical energy source, respectively, and the system is further configured such that during a charging phase, the metal of the metal salt is deposited on the first electrode and oxygen is released on the second electrode, after the charging phase is completed, the first cells of the first electrode and the second electrode are configured to be disconnected from the external energy source, the battery containing the metal deposited on the first electrode remains in a standby state, and during a discharging phase, the second cells of the first electrode and the second electrode are configured to be connected to the positive terminal and the negative terminal of the external energy source, respectively, such that the metal is dissolved from the first electrode and hydrogen is released from the second cell of the second electrode.

17. The two-stage system of claim 16, wherein the solution is an alkaline solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

18. The two-stage system according to claim 17, wherein the zinc salt is selected from the group of salts comprising zincates or zinc hydroxy complexes.

19. The two-stage system of claim 17, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, and titanium, and the second electrode comprises stainless steel, nickel, or a nickel alloy.

20. The two-stage system of claim 16, wherein the solution is an acidic solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

21. The two-stage system of claim 16, wherein the zinc salt is zinc sulfate.

22. The two-stage system of claim 20, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, and titanium, and the first unit of the second electrode comprises titanium metal and further comprises a coating suitable for oxygen release, and the second unit of the second electrode comprises at least one of stainless steel, nickel, a nickel alloy, a graphitized carbon sheet, or a graphitized carbon paper and further comprises a coating suitable for hydrogen release.

23. The two-stage system of claim 1, wherein the solution is configured to be heated during the discharge stage.

24. The two-stage system of claim 23, wherein during the discharge stage, heating the solution is configured to be performed at 80-100°C.

25. The two-stage system of claim 1, wherein the gap between the electrodes is no less than 2 mm.

26. The two-stage system of any one of claims 1-25, wherein the concentration of zinc metal in the solution is maintained at about 100 g / liter.

27. The two-stage system of claim 1, wherein the system further comprises an external power source.

28. A two-stage process for producing hydrogen, the process comprising the steps of: A system is obtained comprising an electrolytic cell comprising a first electrode and a second electrode and a solution comprising a metal salt, wherein the first electrode and the second electrode are connected to an external electrical energy source during a charging phase, thereby depositing zinc metal on the first electrode and releasing oxygen on the second electrode, disconnecting the first electrode and the second electrode after the charging phase, maintaining the cell containing the deposited metal in a standby state, and short-circuiting the first electrode and the second electrode during a discharging phase, thereby dissolving the metal from the first electrode and releasing hydrogen from the second electrode, while substantially not extracting electrical energy.

29. The two-stage process of claim 28, wherein the solution is an alkaline solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

30. The two-stage process according to claim 29, wherein the zinc salt is selected from the group comprising salts of zincates or zinc hydroxy complexes.

31. The two-stage process of claim 29, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, and titanium, and the second electrode comprises stainless steel, nickel, or a nickel alloy.

32. The two-stage method of claim 28, wherein: In the discharge phase, the first and second electrodes are short-circuited and the release of hydrogen from the second electrode occurs without any simultaneous extraction of electrical energy.

33. A two-stage process for producing hydrogen, the process comprising: An electrolytic cell is obtained, the electrolytic cell comprising a first electrode and a second electrode and a solution containing a metal salt, the second electrode being divided into a first unit and a second unit electrically insulated from each other, an external electrical energy source having a negative terminal and a positive terminal is obtained, during a charging phase, the first unit of the first electrode and the second electrode are connected to the negative terminal and the positive terminal of the external electrical energy source, respectively, so that the metal of the metal salt is deposited on the first electrode and oxygen is released from the first unit of the second electrode, and after the charging phase is completed, the first unit of the first electrode and the second electrode are disconnected from the external electrical energy source, thereafter the cell containing the deposited metal is kept in a standby state, and during a discharging phase, the second unit of the first electrode and the second electrode is short-circuited, so that the metal is dissolved from the first electrode and hydrogen is released from the second unit of the second electrode.

34. The two-stage process of claim 33, wherein the solution is an alkaline solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

35. The two-stage process according to claim 34, wherein the zinc salt is selected from the group comprising salts of zincates or zinc hydroxy complexes.

36. The two-stage process of claim 34, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, and titanium, and the second electrode comprises stainless steel, nickel, or a nickel alloy.

37. The two-stage process of claim 33, wherein the solution is acidic, the metal salt is a zinc salt, and the deposited metal is zinc metal.

38. The two-stage process of claim 37, wherein the zinc salt is zinc sulfate.

39. The two-stage process of claim 37, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel and titanium, the first unit of the second electrode comprises titanium metal, optionally provided with a coating suitable for oxygen release, and the second unit of the second electrode comprises at least one of stainless steel, nickel, a nickel alloy and graphitized carbon sheet or graphitized carbon paper and further comprises a coating suitable for hydrogen release.

40. A two-stage process for producing hydrogen comprising the steps of: A system is obtained including an electrolytic cell, wherein the electrolytic cell contains a first electrode and a second electrode and a solution containing a metal salt, an external electrical energy source having a negative terminal and a positive terminal is obtained, the first electrode and the second electrode of the electrolytic cell are connected to the negative terminal and the positive terminal of the external electrical energy source respectively during a charging phase, the first electrode and the second electrode are disconnected from the external electrical energy source after the charging phase is completed, and the first electrode and the second electrode are connected to the positive terminal and the negative terminal of the external energy source respectively during a discharging phase.

41. The two-stage process of claim 40, wherein the solution is an alkaline solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

42. The two-stage process according to claim 41, wherein the zinc salt is selected from the group comprising salts of zincates or zinc hydroxy complexes.

43. The two-stage process of claim 41, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, and titanium, and the second electrode comprises stainless steel, nickel, or a nickel alloy.

44. A two-stage method for producing hydrogen, comprising the steps of: A system is obtained including an electrolytic cell, the electrolytic cell containing a first electrode and a second electrode and a solution containing a metal salt, the second electrode being divided into two units electrically insulated from each other, an external electrical energy source having a negative terminal and a positive terminal is obtained, the first units of the first electrode and the second electrode are connected to the negative terminal and the positive terminal of the external electrical energy source respectively during a charging phase, the first units of the first electrode and the second electrode are disconnected from the external electrical energy source after the charging phase is completed, and the second units of the first electrode and the second electrode are connected to the positive terminal and the negative terminal of the external electrical energy source respectively during a discharging phase.

45. The two-stage process of claim 44, wherein the solution is an alkaline solution, the metal salt is a zinc salt, and the deposited metal is zinc metal.

46. ​​The two-stage process according to claim 45, wherein the zinc salt is selected from the group comprising salts of zincates or zinc hydroxy complexes.

47. The two-stage process of claim 45, wherein the first electrode comprises a metal selected from the group consisting of zinc, copper, stainless steel, and titanium, and the second electrode comprises stainless steel, nickel, or a nickel alloy.

48. The two-stage process of claim 44, wherein the solution is acidic and the metal salt is a zinc metal salt.

49. The two-stage process of claim 48, wherein the zinc metal salt is zinc sulfate.

50. The two-stage process of claim 48, wherein the first electrode comprises a metal selected from the group of zinc, copper, stainless steel and titanium, the first unit of the second electrode comprises titanium and optionally further comprises a coating for oxygen release, and the second unit of the second electrode comprises at least one of stainless steel, nickel, a nickel alloy and graphitized carbon sheet or graphitized carbon paper and further comprises a coating suitable for hydrogen release.

51. The two-stage method of producing hydrogen according to claim 28, wherein the discharge stage further comprises the step of heating the solution to a temperature range higher than the temperature range of the charge stage.

52. The two-stage process of claim 51, wherein the temperature ranges of the charging stage and the discharging stage are 40 to 50°C and 80 to 100°C, respectively.

53. The two-stage process of claim 51, wherein the step of heating the solution comprises use of a heat source selected from the group consisting of an electrical resistance heater, a waste stream, low demand steam, a heat exchanger coil immersed in the solution, an induction heater, or a water jacket.

54. A two-stage process for producing hydrogen according to claim 28, wherein the external energy used in any step of the process is at least partially derived from an energy source comprising one or more of the group consisting of electrical energy, steam energy, power or other industrial equipment or renewable energy.

55. A two-stage method for producing hydrogen according to claim 54, wherein the external energy source is at least partially derived from renewable energy.

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