Hydrogen Production and Chemical Energy Storage

Abstract

A two-stage production of hydrogen is disclosed, comprising an electrolysis cell holding first and second electrodes and a solution containing a metal salt. The first and second electrodes are connected to an external source of electrical energy during a charging stage to deposit metal of the metal salt on the first electrode and release oxygen on the second electrode. Upon completion of the charging stage, the first and second electrodes are disconnected from the external source of electrical energy and the cell holding the deposited metal is held in a standby state until hydrogen production is required. During a discharging stage, the first and second electrodes are shorted, thereby dissolving the metal from the first electrode and releasing hydrogen from the second electrode without simultaneously drawing significant amounts of electrical energy. This increases the amount of hydrogen produced. Variations of the above are also disclosed.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to U.S. Patent Application No. 17 / 742,125, filed May 11, 2022, which is incorporated herein in its entirety.

[0002] [STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT] Not applicable.

[0003] FIELD OF THE PRESENT APPLICATION The present invention relates to hydrogen production and storage of chemical energy, and in particular to methods, systems and devices for producing stored hydrogen and thus providing storage of energy as increased hydrogen potential energy. [Background technology]

[0004] Electrolysis of water to hydrogen and oxygen is a long-established process. As renewable energy mandates continue to be explored, the relatively low availability and reliability of renewable energy sources is a major obstacle. For example, in the case of solar energy, its availability is limited by access to sunlight in a particular region, in a particular season, or in a particular weather pattern. Similarly, in the case of wind energy, the conditions for generating energy from wind sources must be at least adequate, if not optimal, for wind activity in a particular region and at a particular time. Ideally, the ability to "meet demand" means the ability to shift and deploy more power as needed, regardless of the immediate situation. Storage of energy to respond to and meet the changing demand for use of such renewable energy sources at a level sufficient to achieve the targeted renewable energy generation and carbon dioxide emission reductions for public policy is also important for the long-term viability of renewable energy.

[0005] Energy storage for renewable electricity remains a challenge for large-scale operations that need to serve large electrical loads and / or require long periods of operation.

[0006] Efficient systems for enhancing hydrogen production in conjunction with renewable and other power generation and storing energy as hydrogen potential energy until a demand for electrical energy arises are currently very limited but highly desirable. Summary of the Invention

[0007] The present disclosure relates to a method and system for improved electrochemical production of hydrogen, which serves as a useful renewable power resource. Such a system and method provides improved capacity for storing energy as hydrogen energy potential until there is an electrical energy demand that needs to be met. The present disclosure provides for the production of hydrogen using electrochemical reactions in a specially adapted environment. In an embodiment of the present disclosure, a method and system for hydrogen production is provided, which uses two stages in its operation. The system includes a first and second electrode and an electrolytic cell that holds a solution. The solution, which may be an aqueous acidic or alkaline solution, may hold salts of various metals, each of which may dissolve via hydrogen release as an electron balance reaction. Thus, the present invention may operate with a solution that holds metal cations such as iron, nickel, manganese, zinc, tin, and lead. However, the applicant has discovered that a system with even better efficiency is obtained when the solution of metal salts is zinc-based. Thus, for simplicity, the remainder of this specification will only refer to zinc solutions, although other metals as indicated above may be used. The first electrode can be made of a metal or metal alloy, such as zinc, copper, stainless steel, or titanium, and the second electrode can be made of one or more of stainless steel, nickel and its alloys, titanium and its alloys, or graphitized carbon sheets or tissues optionally provided with a suitable catalytic coating to reduce the overpotential for 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 cell (see FIG. 1) containing the solution of zinc salt, the first and second electrodes are connected to an external source of electrical energy, which may be a renewable source such as solar or wind power. A flow of electrons, assisted by the external power source, is supplied to the first electrode where the zinc of the zinc salt is reduced. The electrons supplied to the first electrode are withdrawn from the second electrode where oxygen is released via the electro-oxidation of water. Once the charging phase is completed, the first and second electrodes are isolated from the external energy source (see FIG. 2).In this standby state, the applicant has found that the zinc remains extremely stable since its surface is characterized by a high reduction potential compared to the standard hydrogen electrode (SHE), which prevents significant oxidation of the zinc metal. When hydrogen is required, i.e. during the discharge phase of operation, the known prior art connects the first and second electrodes to an external resistive electric circuit that allows electrons to flow from the first electrode, and the zinc dissolves by oxidation and produces hydrogen by electroreduction of water on its surface towards the second electrode. The release of hydrogen on the second electrode is facilitated by the reduced HER overpotential, as already mentioned, characterizing the material used for the construction of the second electrode. This electric device accelerates the hydrogen release, and electrical energy is simultaneously withdrawn from the cell via the external resistive circuit to perform work or to be stored. However, the applicant has found that the hydrogen release rate allowed by such known prior art devices is too low to be compatible with the type of large-scale application that is the object of the present invention. Surprisingly, the applicant has found that a serious obstacle can be overcome when the external electronic circuit is short-circuited (see FIG. 3). The short circuit does not allow electrical energy to be extracted through an external resistive circuit as in prior art devices, or at least reduces the residual electrical energy released in the second stage to less than 1% of the available energy of the zinc-hydrogen reaction. However, applicant has discovered that this loss of externally available electrical energy is more than compensated for by the increased hydrogen release rate, which allows for a significant reduction in the electrode area required to produce the amount of hydrogen to be supplied to large-scale applications. This results in a reduced electrode area, which leads to a significant reduction in the required capital investment. Applicant has also discovered 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 the concentration of metallic zinc in the range of 90-110 grams / liter, preferably 95-105, and more preferably 100 grams / liter.

[0008] In another embodiment of the present disclosure (see Figs. 4, 5 and 6), a hydrogen production system and method is provided in which two stages are used. The system includes an electrolysis cell having a first electrode comprising a metal selected from the group consisting of zinc, copper, stainless steel or titanium, and a second electrode divided into two units electrically insulated from each other. The first unit of the second electrode may comprise titanium metal having a coating adapted for oxygen release. The second unit of the second electrode may comprise nickel, nickel alloy, stainless steel or a graphitized carbon material such as a sheet or tissue, both of which have a selective coating to facilitate hydrogen release. The cell contains a solution carrying a zinc salt. During a charging stage (see Fig. 4), the first unit 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 unit of the second electrode, which is characterized by a low OER overpotential. When the charging stage is completed, the first unit of the first electrode and the second electrode are isolated from the external energy source. In the next waiting state (see FIG. 5), the applicant has found that the zinc is substantially stable due to the low rate of the binding reaction of hydrogen release, which is in fact characterized by a very high overpotential on the zinc surface. When hydrogen is required at a certain release rate, i.e. during the discharge phase of operation (see FIG. 6), the first electrode and the second unit of the second electrode are connected to an external short circuit, so that hydrogen is released on the surface of the second unit of the second electrode, characterized by an HER overpotential, while the zinc is dissolved. By means of the external short circuit, a hydrogen release rate suitable for large-scale applications, which is the object of the present invention, is obtained, with all the advantages of the reduction of the electrode surface and the capital investment requirements mentioned above.

[0009] In a further embodiment of the present disclosure, a hydrogen production system and method are provided (see Figs. 7, 8 and 9). Two stages are employed. The system includes an electrolysis cell with first and second electrodes and filled with a solution containing a zinc salt. The system further includes connecting the negative and positive terminals to an external electrical energy source provided. In a charging stage (see Fig. 7), the first and second electrodes are connected to the negative and positive terminals of the external electrical energy source, respectively. In the charging stage, zinc is deposited on the first electrode and oxygen is released on the second electrode. When the charging stage is completed, the first and second electrodes are disconnected from the external energy source and the cell is kept in a standby state until hydrogen production is required (see Fig. 8). When hydrogen is required, i.e., in a discharging stage, the first and second electrodes are again connected to the opposite terminals of the external energy source, i.e., the first electrode with the zinc deposition is connected to the positive terminal and the second electrode is connected to the negative terminal (see Fig. 9). Zinc is dissolved from the first electrode and hydrogen is released on the second electrode at a rate that 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, is raised to a value higher than would be tolerated by simple short circuit operation.

[0010] In a further embodiment of the present disclosure, a hydrogen production system and method are provided. In this embodiment, the applicant has discovered that the hydrogen production rate can be further increased if the electrolyte is heated during the discharge stage in addition to the above process (see FIG. 10). The applicant has determined that heating of the solution can come from multiple available sources, such as, for example, a resistance heater, a waste energy stream, or a low demand steam source such as a heat recovery steam generator (HRSG). It is noted that sources that allow both positive (and alternating) heating and cooling of the solution, such as a heat exchanger coil immersed in the solution, an electric resistance heater, an induction heater, or a water jacket, may be ideal for this aspect of the present disclosure.

[0011] Additionally, the hydrogen release rate in the shorting electrode device of the present invention may be affected or hindered by the electrode distance and the internal resistivity of the solution. It is most preferred that the electrode distance is reduced to 1.75-3.25 mm, preferably 2-3 mm, to ensure 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. The internal resistivity of the solution may be substantially reduced by increasing the temperature of the cell, in addition to using a high zinc salt concentration, as suggested above. Indeed, applicants have found that increasing the cell temperature to 35-55°C, preferably 37.5-52.5°C; and more preferably to 75-105°C; preferably 77.5-102.5°C; and more preferably to 80-100°C, over the typical 40-50°C range during the charge phase, during the discharge phase, allows for a substantial increase in the hydrogen release rate, resulting in a further reduction in both the required electrode area and the associated capital investment. Applicants have also found that, after the discharge step is complete, it is preferable to restore the cell temperature to the lower temperature level used in the charge step in order to deposit zinc metal with the highest efficiency. Heating the solution may result in a slight decrease in charging efficiency, but losses can be preferably minimized by applying a heat exchanger.

[0012] These and other features of the present disclosure are explained in further detail in the following description. [Brief description of the drawings]

[0013] [Figure 1] Disclosed is a schematic diagram of one embodiment of a charging stage of a process for hydrogen production that includes the use of an external power source, a cell holding first and second electrodes connected to the external source, and a solution holding a zinc salt that facilitates deposition of zinc metal on the first electrode and enables release of oxygen on the second electrode. [Diagram 2] A schematic diagram of an embodiment shown in FIG. 1 is disclosed in which, after the charging phase is completed, the cell with the first and second electrodes isolated from the external source and holding the deposited zinc metal is kept in standby until hydrogen production is required. [Diagram 3] A schematic diagram of one embodiment of a discharge stage of a process for hydrogen production is disclosed that includes shorting the first and second electrodes of FIGS. 1 and 2 such that zinc metal is oxidatively dissolved from the first electrode and hydrogen is released on the second electrode at an increased rate without the production of significant electrical energy. [Figure 4] 1 shows a schematic diagram of an alternative embodiment of an electrolysis cell according to the present disclosure, in which the second electrode includes first and second units that are electrically insulated from each other. [Diagram 5] 1 shows a schematic diagram of an alternative embodiment of an electrolysis cell according to the present disclosure, in which the second electrode includes first and second units that are electrically insulated from each other. [Figure 6] 1 shows a schematic diagram of an alternative embodiment of an electrolysis cell according to the present disclosure, in which the second electrode includes first and second units that are electrically insulated from each other. [Figure 7] 1 is a schematic diagram of an alternative embodiment of a discharge stage of a process for producing hydrogen, the alternative embodiment including a step of reversing the polarity utilized in the charge stage of the process according to the embodiment of FIG. [Figure 8] 2 is a schematic diagram of an alternative embodiment of the discharge stage of the process for producing hydrogen, which includes reversing the polarity utilized in the charge stage of the process according to the embodiment of FIG. 1. Waiting is shown in the alternative embodiment. [Figure 9] 2 is a schematic diagram of an alternative embodiment of the discharge stage of a process for producing hydrogen, the alternative embodiment including a step of reversing the polarity utilized in the charge stage of the process according to the embodiment of FIG. 1. Discharging in the alternative embodiment is shown. [Figure 10] FIG. 10 is a schematic diagram of a further alternative embodiment of a discharge stage of a process for hydrogen production that includes heating a solution of zinc metal salt to 80-100° C. in addition to shorting the first and second electrodes.

[0014] Corresponding reference characters are used for corresponding elements as set forth in the description and drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The following detailed description describes the claimed disclosure by way of example and not by way of limitation. The specification illustrates and enables a person skilled in the art to make and use the claimed disclosure, and describes several embodiments, adaptations, variations, alternatives, and uses of the claimed disclosure. Furthermore, it is to be understood that the claimed disclosure is not limited in its application to the details of the systems, methods, and devices specifically described in the following description or illustrated by the drawings. The claimed disclosure is capable of other embodiments and can be practiced or carried out in various ways. It is also to be understood that the phrases and terms used herein are for the purpose of description and should not be regarded as limiting.

[0016] As used herein, the term "cell" refers to a container consisting of a first electrode, a second electrode, and optionally more electrodes, said second electrode being optionally divided into first and second electrically isolated units, and a solution, preferably an aqueous solution, containing dissolved metal salts, preferably zinc salts, and optionally other dissolved species, such as additives suitable for promoting metal deposition and preventing dendrite growth.

[0017] As used herein, the term "electrode" refers to a conductor from which electrons (electricity) are supplied or withdrawn and which participates in a reaction at the electrode surface with chemical species present in the solution contained in the cell. For example, in the charging phase of the present disclosure, a flow of electrons to the first electrode is generated by an external source of electrical energy. At the interface of the first electrode surface and the solution, a reduction reaction occurs in which the electrons combine with zinc ions present in the solution, leading to zinc deposition (Zn 2+ +2e -→Zn). An external energy source acting as a kind of electron pump transfers electrons from the second electrode that are produced from an oxidation reaction that occurs at the interface between the second electrode and the solution. This reaction produces oxygen (O 2 ) and OH held in solution in water - It is expressed by the conversion of ions (2OH - →0.5O 2 +H 2 O+2e - ). Alternatively, this reaction can be carried out with oxygen (O 2 ) and H + is expressed by the conversion of water in an aqueous solution to (H 2 O → 0.5O 2 +2H + +2e - ).

[0018] As used herein, the term "catalyst" refers to any compound that facilitates a given reaction. As used in this document, the term catalyst describes the ability of the surface of the second electrode to facilitate the oxygen releasing reaction, the hydrogen releasing reaction, or both, which in electrochemical word choice refers to the ability to reduce the overpotential of the reaction.

[0019] As used herein, the term "large scale hydrogen production" or "large scale chemical storage resource" refers to the amount of hydrogen or hydrogen potential required to support the operation of a power system in the range of several kW power, preferably at least 1 MW power.

[0020] Applicants have herein devised a two-stage method, system and device that can greatly improve the production of hydrogen and serve as a chemical energy storage resource for large-scale renewable power operations. Moreover, the improved capacity to store such hydrogen energy potential greatly improves the ability to time the utilization of such energy potential when it is most needed. The present disclosure produces hydrogen using metal deposition / dissolution reactions, particularly zinc deposition / dissolution reactions, and oxygen / hydrogen release reactions in a specially adapted environment designed to increase the rate of hydrogen production using a two-stage system. Generally, during the charging phase, an external source of electrical energy is connected to the first and second electrodes of a cell that holds a solution of zinc salts. In particular, the first electrode is connected to the negative polarity of the external source and the second electrode is connected to the positive polarity, thus establishing a voltage difference potential across the cell. This voltage difference allows an electric current to move through the cell, and the higher the current, the higher the voltage difference, causing zinc metal held in solution to deposit as zinc salts on the first electrode and oxygen to be released on the second electrode. Once the charging phase is completed, the first and second electrodes are disconnected from the external energy source and the cell is held in standby until hydrogen production is required. The time the cell is held in standby can vary widely from virtually instantaneous to 12 hours or even substantial durations such as days, weeks or more. There are no practical limitations beyond the demand leading to the withdrawal of stored hydrogen and the economics of the need for a hydrogen storage facility of a certain size. In the discharging phase, when hydrogen production is required, zinc metal is oxidatively dissolved and redissolved from the first electrode and hydrogen is produced at the second electrode by shorting the first and second electrodes without drawing any or very little power from the system, contrary to what is disclosed in the known prior art. The applicant has surprisingly discovered that shorting the first and second electrodes significantly increases the rate of hydrogen production by directing all the available energy potential of the cell, represented by the zinc dissolution reaction, towards the hydrogen release reaction. As an example, the applicant has developed a 400m 3 / (time × m of electrode surface 2) rate of hydrogen release, which is 350 m 2 This allows one to meet the production of hydrogen per hour requirements of a 1 MW power plant with limited electrode surface of 1000 kcal / hour. The range of overvoltages that must 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 will be known to one skilled in the art without undue experimentation.

[0021] The first and second electrodes of the cell can have a gap of 1.75 to 4.25, preferably 2 to 3, and the solution can hold 50 to 70, preferably 55 to 65, most preferably 60 grams per liter of metal cation in the preferred case of zinc metal. The applicant has surprisingly found that it is particularly advantageous to combine said short circuit operation with both increasing the concentration of zinc metal salt in the solution to reduce the electrical resistivity and improve mass transport, e.g. up to 100 grams per liter of zinc cation, and reducing the electrode gap to a low gap of e.g. 2 to 3 mm. This still allows problem-free operation without the risk of any internal short circuit between the first and second electrodes due to the growth of metal dendrites. Such a combination leads to the production of hydrogen at an even higher rate than with a simple short circuit. By way of example, using a device including a short circuit, high metal salt concentration, and reduced electrode gap, the applicant has found that the rate of hydrogen production can be increased to about 550 m 3 / (time × m of electrode surface 2 ), which is about 280m 2This corresponds to the hydrogen production per hour required by a 1 MW power plant having a limited electrode surface of 1000 W. As disclosed further below, applicant has developed additional mechanisms to enhance hydrogen production through various alternatives and combinations to the disclosed two-stage hydrogen production theme. Thus, applicant has provided a significant increase in hydrogen potential energy for use as a chemical storage resource. In all of the two-stage systems disclosed herein, the cells of the system can be configured to be connected to a separate external power source, or the system can be configured so that an external power source is incorporated as an integral part of the system.

[0022] 1, 2 and 3, a hydrogen production system 100 is provided in a first embodiment of the present disclosure. As indicated above, two operation stages are employed: a charging stage (see FIG. 1), a standby state separating the charging and discharging stages (see FIG. 2), and a discharging stage (see FIG. 3). The system 100 includes an electrolysis cell 200 holding first and second electrodes 10, 20. The cell 200 is filled with a solution 30 holding a zinc salt 40. During the charging stage of operation (see FIG. 1), the first and second electrodes 10, 20 are connected to an external electrical energy source 300. During this charging stage, zinc metal 50 is deposited on the first electrode 10 and oxygen 60 is released from the second electrode 20. Once the charging stage is complete, the first and second electrodes 10, 20 are disconnected from the external energy source 300 and the charged cell holding the deposited zinc metal is kept in a standby state (see FIG. 2) until hydrogen production is required. When hydrogen is required, i.e., during the discharge phase of operation (see FIG. 3), the first and second electrodes 10, 20 are shorted together, zinc metal 50 dissolves from the first electrode 10 reforming the metal salts in solution, and hydrogen 70 is released onto the second electrode 20. Thus, with reference to FIG. 3, the discharge phase of operation involves shorting the first and second electrodes 10, 20 together.

[0023] The solution 30 in the electrolytic cell 200 may be alkaline or acidic. If the solution is alkaline, the zinc metal salt 40 will be, for example, zincate (ZnO 22- ) or zinc hydroxyl complex (Zn(OH) 4 2- ), but is not limited to, zinc as a complex compound such as zinc sulfate, if the solution is acidic. The use of an acidic or alkaline solution is not secondary. If an acidic solution is used with zinc sulfate as the zinc salt, it may be prone to partially separated zinc precipitation and dendrite growth. This reduces the efficiency of the system and leads to the risk of internal shorting of the first and second electrodes. An alkaline solution reduces metal precipitation and dendrite growth, allows operation with a smaller electrode gap, and ensures better efficiency. The alkaline solution also serves to stabilize the system, so that the use of a single second electrode is considered feasible (see below for a discussion of an alternative embodiment using a second electrode split into two electrically isolated first and second units). In fact, if the solution used is alkaline, the second electrode is preferably made of nickel or a nickel alloy. These materials are suitable for operation both in the charge phase, where oxygen is released at low overpotentials, and in the discharge phase, where hydrogen is released at similarly low overpotentials. Moreover, these materials are characterized by a suitable chemical stability against corrosive attack. In the above embodiment using alkaline solutions, it is expected that corrosion will also be minimized if the second electrode is made of high surface area nickel, such as sandblasted nickel or thermally sprayed nickel, which is particularly efficient in further lowering the overpotential.

[0024] If the solution is acidic, in addition to the already discussed effects of separation precipitation and growth of dendrites, the operation may be seriously impaired by the deterioration of the performance of the second electrode. Indeed, as taught by the available prior art, resistance to corrosive attack during the charging phase through oxygen release appears achievable if the second electrode is made of titanium or titanium alloy with a catalytic coating. However, such a second electrode is inoperable during the discharging phase, during which hydrogen is released. In fact, titanium becomes embrittled due to hydrogen penetration in the metal lattice and is not suitable for safe hydrogen production in acidic solutions. Stainless steel and nickel and nickel alloys are suitable for use as second electrodes during the discharging phase through hydrogen release, but are subject to severe corrosion during the charging phase through oxygen release. The applicant has discovered that the negative characteristics can be overcome by adopting a second electrode divided into two electrically insulated units, as will be described below.

[0025] With reference to Figures 4, 5 and 6, an embodiment 100 of an alternative two-stage hydrogen release system and method is depicted. In this alternative embodiment, as in the embodiment shown in Figures 1, 2 and 3, an electrolysis cell 200 includes two electrodes 10, 20. Preferably, the first electrode is made of zinc, copper, stainless steel or titanium. In an alternative embodiment to the disclosed system for hydrogen release, the second electrode 20 is divided into two units 20a, 20b that are electrically insulated from each other. The first unit 20a of the second electrode 20 is preferably titanium metal with a coating adapted for oxygen release. Such coatings include noble metals and noble metal oxides, in particular mixed iridium and tantalum oxides as disclosed in the patent literature. The second unit of the second electrode is preferably made of stainless steel, nickel, nickel alloys and graphitized carbon sheet or tissue, preferably provided with a coating adapted for hydrogen release. Such coatings include noble metals such as ruthenium and platinum. The cell 200 contains a solution containing zinc salts, which is particularly an acidic solution, and the use of a single-structure second electrode is characterized by serious operational problems, as previously expected. During the charging phase (see FIG. 4), the first electrode 10 and the first unit 20a of the second electrode 20 are connected to an external electrical energy source 300. During this phase, zinc metal 50 is deposited on the first electrode 10 and oxygen 60 is released from the first unit 20a of the second electrode 20. When the charging phase is completed, the first electrode 10 and the first unit 20a of the second electrode 20 are disconnected from the external electrical energy source 300 and the cell 200 remains in a standby state until hydrogen production is required, i.e., until the discharging phase is initiated (see FIG. 5). During the discharging phase (see FIG. 6), the first electrode 10 and the second unit 20b of the second electrode 20 are short-circuited, so that the second unit 20b of the second electrode 20 releases hydrogen 70 at a high rate and the zinc metal 50 dissolves from the first electrode 10. Thus, in this alternative embodiment, the first unit 20a of the second electrode 20 is kept disconnected during the discharge phase. In addition to the advantage of releasing hydrogen at a high rate, this alternative embodiment has the advantage of less wear and a longer service life for the second electrode unit.When a single second electrode 20 is used, oxygen and hydrogen production occurs on the same electrode, resulting in large periodic voltage fluctuations and accelerated corrosion. This device also prevents hydrogen production on titanium electrodes, which have been shown to become embrittled in acidic environments during hydrogen production. Unit 20a is used only for oxygen production, and unit 20b is used only for hydrogen production, significantly extending the service life of the two units.

[0026] Further alternative embodiments of the present disclosure also include a two-stage system and method for improved production of hydrogen. Referring to Figures 7, 8 and 9, the system 100 includes an electrolysis cell 200 holding first and second electrodes 10, 20 and filled with a solution 30 holding a zinc salt 40. The system further includes an external electrical energy source 300 holding terminals of the negative electrode 300a and the positive electrode 300b. During the charging phase, the first and second electrodes 110 and 220 are connected to the negative and positive electrode 300a and 300b terminals of the external electrical energy source 300, respectively. During the charging phase, zinc metal 50 is deposited on the first electrode 10 and oxygen 60 is released on the second electrode 20. Once the charging phase is completed, the first and second electrodes 10 and 20 are separated from the external source 300 and the cell is kept in a standby state until hydrogen production is required, which occurs during the discharging phase. In the discharge phase, the first and second electrodes 10, 20 are again connected to oppositely charged terminals of the external energy source 300, i.e. the first electrode 10 is again connected to the positive terminal 300b and the second electrode 20 is again connected to the negative terminal 300a of said external source 300. Zinc metal 50 dissolves from the first electrode 10 and hydrogen 70 is released on the second electrode 20. The rate of hydrogen production is greatly increased with respect to the typical rate of simple short circuit conditions of the embodiment shown in Figures 1, 2 and 3, although this advantage is partially diminished by some additional power consumption. Furthermore, hydrogen production can be controlled by controlling the voltage of the external source 300 in the discharge phase.

[0027] In a further embodiment, hydrogen release is significantly increased by heating the solution during the discharge phase, where the increase in solution temperature serves to significantly reduce both the internal resistance of the solution and the overpotential for hydrogen production on the second electrode (see FIG. 10). Applicant has discovered that a significant increase in hydrogen release rate is possible by increasing the cell temperature over the initial charge phase range of 35-55°C, preferably 37.5-52.5°C; and more preferably 40-50°C, to 75-105°C; preferably 77.5-102.5°C; and more preferably 80-100°C, during the discharge phase. This further reduces both the required electrode surface and the associated capital investment. Applicant has also discovered that after the discharge phase is complete, the cell temperature should preferably be restored to the low temperature level used during the charge phase in order to deposit zinc metal with the most efficient efficiency. For example, heating during the discharge phase, for example in the preferred range of 80-100°C, significantly increases the hydrogen release rate, thereby further reducing both the required electrode surface and the associated capital investment. After the discharge step is complete, the cell temperature must be returned to the temperature level used for the charge step, e.g., 40-50°C, in order to deposit zinc metal with the best efficiency. As noted above, heating the solution causes a small loss of efficiency, but this can be minimized by applying a heat exchanger between the cells.

[0028] In view of the above, it will be seen that the several objects and advantages of the disclosure are achieved and other advantageous results attained.

[0029] Since various changes may be made in the above configurations 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 be interpreted as illustrative and not in a limiting sense.

Claims

1. 1. A two-stage system for hydrogen production, the system comprising: an electrolysis cell comprising first and second electrodes and a solution comprising a metal salt, the first and second electrodes configured to be connected to an external electrical energy source, 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 when the charging phase is completed, the first and second electrodes are configured to be isolated from the external energy source, the cell holding the deposited metal on the first electrode is configured to hold a standby state, and during a discharging phase, the first and second electrodes are configured to be short-circuited, such that the metal is dissolved from the first electrode and hydrogen is released on the second electrode.

2. 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. 3. The two-stage system of claim 2, wherein the zinc salt is selected from the group consisting of a zincate salt or a zinc hydroxyl complex.

4. 3. 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 nickel alloys.

5. 1. A two-stage system for hydrogen production, the system comprising: an electrolytic cell holding a first electrode, a second electrode, the second electrode being divided into first and second units electrically insulated from each other, and a solution holding a metal salt, the first unit of the first electrode and the second electrode being configured to be connected to an external electrical energy source during a charging phase, whereby the metal of the metal salt is deposited on the first electrode and oxygen is released on the first unit of the second electrode, the first unit of the first electrode and the second electrode being configured to be disconnected from the external electrical energy source upon completion of the charging phase, the cell holding the deposited metal on the first unit of the second electrode being configured to be held in a standby state, and the second unit of the first electrode and the second electrode being configured to be short-circuited during a discharging phase, whereby the deposited metal is dissolved from the first electrode and hydrogen is released on the second unit of the second electrode.

6. 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. 7. The two-stage system of claim 6, wherein the zinc salt is selected from the group consisting of a zincate salt or a zinc hydroxyl complex.

8. 7. 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 nickel alloys.

9. 6. 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. 10. The two-stage system of claim 9, wherein the zinc salt is zinc sulfate.

11. 10. 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, the first unit of the second electrode comprises titanium metal and further comprises a coating layer adapted for selective oxygen release, and the second unit of the second electrode comprises stainless steel, nickel, and nickel alloys, and graphitized carbon sheet or tissue, and further comprises a coating layer adapted for selective hydrogen release.

12. 1. A two-stage system for hydrogen production, the system comprising: first and second electrodes and an electrolysis cell holding a solution comprising a metal salt, the system configured to be connected to an external electrical energy source having a negative polarity and a positive polarity, the first and second electrodes configured to be connected to the negative and positive terminals of the external electrical energy source, respectively, 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, the first and second electrodes configured to be isolated from the external energy source upon completion of the charging phase, the cell holding the deposited metal on the first electrode is configured to be held in a standby state, and during a discharging phase, the first and second electrodes configured to be connected to the positive and negative terminals of the external electrical energy source, respectively, such that the metal is dissolved from the first electrode and hydrogen is released on the second electrode.

13. 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. 14. The two-stage system of claim 13, wherein the zinc salt is selected from the group consisting of a zincate salt or a zinc hydroxyl complex.

15. 14. 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. 1. A two-stage system for hydrogen production, the system comprising: an electrolysis cell holding a first electrode, a second electrode, the second electrode being divided into first and second units electrically insulated from each other, a solution containing a metal salt, and an external electrical energy source having a negative and positive polarity, the first unit of the first electrode and the second electrode being configured to be connected to the negative and positive terminals of the external electrical energy source, respectively, the system being 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, when the charging phase is completed, the first unit of the first electrode and the second electrode are configured to be separated from the external energy source, the cell holding the deposited metal on the first electrode is kept in a standby state, and during a discharging phase, the second unit of the first electrode and the second electrode are configured to be connected to the positive and negative terminals of the external source, respectively, such that the metal is dissolved from the first electrode and hydrogen is released on the second unit of the second electrode.

17. 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. 20. The two-stage system of claim 17, wherein the zinc salt is selected from the group consisting of a zincate salt or a zinc hydroxyl complex.

19. 20. 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. 17. 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. 17. The two-stage system of claim 16, wherein the zinc salt is zinc sulfate.

22. 21. 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, the first unit of the second electrode comprises titanium metal and further comprises a coating layer adapted 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 tissue and further comprises a coating layer adapted for hydrogen release.

23. The two-stage system of claim 1 , wherein the solution is configured to heat during the discharging stage.

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

25. 10. The two-stage system of claim 1, wherein the gap between the electrodes is a minimum of 2 mm.

26. The two-stage system of any one of claims 1 to 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 the external power source.

28. 1. A two-stage method for producing hydrogen, the method comprising the steps of obtaining a system including an electrolytic cell holding first and second electrodes and a solution including a metal salt; during a charge stage, connecting the first and second electrodes to an external source of electrical energy, thereby depositing zinc metal on the first electrode and releasing oxygen on the second electrode; upon completion of the charge stage, separating the first and second electrodes; holding the cell holding the deposited metal in a standby state; during a discharge stage, shorting the first and second electrodes together, thereby dissolving the metal from the first electrode; and during a discharge stage, substantially simultaneously withdrawing electrical energy and releasing hydrogen from the second electrode.

29. 30. The two-step method 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. 30. The two-step method of claim 29, wherein the zinc salt is selected from the group consisting of a zincate salt or a zinc hydroxyl complex.

31. 30. The two-step method 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. 30. The two-stage method of claim 28, wherein the step of releasing the hydrogen from the second electrode during the discharging step of shorting the first and second electrodes occurs without selectively withdrawing electrical energy simultaneously.

33. 1. A two-stage method for hydrogen production, the method comprising the steps of: obtaining an electrolysis cell holding a first electrode and a second electrode separated into first and second units electrically insulated from each other, and a solution containing a metal salt; obtaining an external electrical energy source having negative and positive terminals; connecting the first unit of the first and second electrodes to the negative and positive terminals of the external electrical energy source, respectively, during a charging stage, thereby depositing the metal of the metal salt on the first electrode and releasing oxygen on the first unit of the second electrode; and, upon completion of the charging stage, holding the cell holding the deposited metal in a standby state after separating the first unit of the first and second electrodes from the external source; and, during a discharging stage, shorting the second unit of the first and second electrodes, thereby dissolving the metal from the first electrode and releasing hydrogen from the second unit of the second electrode.

34. 34. The two-step method 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. 35. The two-step method of claim 34, wherein the zinc salt is selected from the group consisting of a zincate salt or a zinc hydroxyl complex.

36. 35. The two-step method 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. 34. The two-step method of claim 33, wherein the solution is acidic, the metal salt is a zinc salt, and the deposited metal is zinc metal.

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

39. 38. The two-step method 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 layer adapted for oxygen release, and the second unit of the second electrode comprises at least one of stainless steel, nickel, nickel alloy, and graphitized carbon sheet or tissue, further comprising a coating layer adapted for hydrogen release.

40. 1. A two-stage method for hydrogen production, comprising the steps of: obtaining a system including an electrolytic cell holding first and second electrodes and a solution including a metal salt; obtaining an external electrical energy source having negative and positive terminals; connecting the first and second electrodes of the electrolytic cell to the negative and positive terminals, respectively, of the external electrical energy source during a charging stage; isolating the first and second electrodes from the external energy source upon completion of the charging stage; and connecting the first and second electrodes to the positive and negative terminals, respectively, of the external energy source during a discharging stage.

41. 41. The two-step method 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. 42. The two-step method of claim 41, wherein the zinc salt is selected from the group consisting of a zincate salt or a zinc hydroxyl complex.

43. 42. The two-step method 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. 1. A two-stage method for hydrogen production, comprising the steps of: obtaining a system including a first electrode and a second electrode separated into two units electrically insulated from each other, and an electrolytic cell holding a solution including a metal salt; obtaining an external electrical energy source having negative and positive terminals; during a charging phase, connecting the first unit of the first electrode and the second electrode to the negative and positive terminals of the external electrical energy source, respectively; isolating the first unit of the first electrode and the second electrode from the external electrical energy source upon completion of the charging phase; and during a discharging phase, connecting the second unit of the first electrode and the second electrode to the positive and negative terminals of the external electrical energy source, respectively.

45. 45. The two-step method 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. 46. ​​The two-step method of claim 45, wherein the zinc salt is selected from the group consisting of a zincate salt or a zinc hydroxyl complex.

47. 46. ​​The two-step method 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. 45. The two-step method of claim 44, wherein the solution is acidic and the metal salt is a zinc metal salt.

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

50. 49. The two-step method of claim 48, 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 and optionally comprises a coating adapted for oxygen release, and the second unit of the second electrode comprises at least one of stainless steel, nickel, a nickel alloy, and a graphitized carbon sheet or tissue and further comprises a coating layer adapted for hydrogen release.

51. 30. The two-stage method for hydrogen production of claim 28, wherein the discharging stage further comprises heating the solution to a higher temperature range than the temperature range of the charging stage.

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

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

54. 30. The two-stage method for hydrogen production as described in claim 28, wherein the external energy source for any step of the method is derived at least in part from an energy source including any one or more of the group consisting of an electrical energy source, a steam energy source, a power or other industrial plant, or a renewable energy source.

55. 55. The two-stage method for hydrogen production according to claim 54, wherein the external energy source is derived at least in part from a renewable energy source.

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