METHOD AND SYSTEM FOR ELECTROCHEMICAL HYDROGEN GENERATION

Abstract

An apparatus, a system and a method for electrochemical generation of hydrogen are disclosed. The apparatus may include a cathode, a polymer electrolyte membrane surrounding the cathode and a housing surrounding the polymer electrolyte membrane. The housing may include an anode electrically connected to the cathode. The system for electrochemical generation of hydrogen may include a water purifier in fluid communication with a hydrogen generating unit, an electrolyte source in fluid communication with the hydrogen generation unit and a power source electrically connected to the hydrogen generating unit. The method may include passing water and electrolyte into the hydrogen generation unit and applying a voltage between the anode and the cathode to generate hydrogen gas.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional application No. 61/317,014, filed on Mar. 24, 2010, the disclosure of which is hereby expressly incorporated by reference in its entirety and is hereby expressly made a portion of this application.

FIELD OF THE INVENTION

The present disclosure relates to a method and system for the generation of hydrogen. Various methods, features and system configurations are discussed.

BACKGROUND OF THE INVENTION

A water electrolyzer is an energy conversion device where water and electricity are used as fuel in order to produce hydrogen and oxygen. This energy breaks bonds between hydrogen and oxygen atoms with the use of a catalyst (Eq.1).

H₂O+electrical current→H₂+½O₂   (Eq. 1)

Several applications exist for low flow water electrolyzers. These include, continuous supply of H₂ to gas chromatographs and other analytical instrumentation, materials processing, chemical synthesis, smelting, heavy hydrogen production and weld gas applications.

New hydrogen generation technologies are being driven by the move towards the use of hydrogen as an energy carrier. It is envisioned that hydrogen may replace petroleum based fuels in automobiles and electrical generators. A primary objective is the use of sustainable energy sources in combination with water electrolyzers to produce hydrogen fuel. For this to be economically viable, highly energy efficient, low cost hydrogen generator systems are needed.

Aside from hydrogen fuel stations and electrical generation plants, several other applications exist for hydrogen production at moderate to large scales. These include, on-site ultra-high purity (UHP) hydrogen production for silicon epitaxy, hydrogen for metalorganic chemical vapor deposition (MOCVD) of compound semiconductors, hydrogen for solar cell manufacturing, and hydrogen cooling gas for power plant generators, food processing and home heating. For on-site ultra-high purity hydrogen production, a purity of 99.9995% H₂ is obtained. Such systems are operated at a pressurization of 200-450 psig, with high system durability, low temperature operation, and nominal space requirements as desirable attributes.

Several electrochemical hydrogen generation technologies are known, such as described in the teachings of U.S. Pat. Nos. 6,613,215, 6,685,821, 6,939,449 and 7,270,908, which are each hereby incorporated by reference for this purpose and in their entireties. Current literature indicates that alkaline based electrolyzers are the most efficient. These systems utilize a potassium hydroxide electrolyte where the reaction chemistry is initiated by reaction of hydroxide ion at the anode followed by hydrogen production at the cathode (Equations 2-3).

Anode 4OH⁺→O₂+2H₂O+4e⁻  (Eq. 1)

Cathode 2H₂O+2e⁻→H₂+2OH⁻  (Eq. 2)

Though these systems look very promising, many practical problems have been encountered in attempts to implement this technology. Current polymer electrolyte membrane (PEM) and alkaline system designs lack durability and are prone to mechanical failure. This in part is due to the vast number of mechanical parts contained in these systems. These include, tightly compressed bipolar plates, catalyst materials in the form of thin sheets, water maintenance systems, fragile graphite pads, membrane support screens, cell frames, flow field management systems and compression maintenance systems. The requirement for many of these parts and sub-systems can be attributed to the inefficient flat plate design. The use of a membrane as the primary electrolyte for PEM electrolyzers places undue burden on the entire system. In addition, these cells suffer from high material cost including platinum or palladium catalysts which are required to lower activation barriers and speed up reaction kinetics. In general, a flat plate design makes scale up difficult due to size, weight and number of seals. This leads to frequent field failures and poor reliability. Moreover, flat plate designs are not cost effective for scale up to high hydrogen production rates.

A cost model published by the National Renewable Energy Laboratory (NREL) (NREL/MP-560-36734), which is hereby incorporated by reference in its entirety, shows that capital equipment costs are very significant for small to midsize H₂ generators for vehicle re-fueling applications. Neighborhood re-fueling stations servicing 5-50 cars are estimated to require H₂ generation at a rate of 100 slm. Small re-fueling stations (small forecourt) are estimated to require H₂ generation at 1000 slm. Most significant are the capital equipment costs associated with these applications where it is estimated that 73% of the cost of produced hydrogen for the neighborhood refueling station is associated with capital costs. Moreover, 55% of the cost of produced hydrogen is associated with capital equipment for the small refueling station (small forecourt). System energy efficiencies range from 56% for PEM systems to 73% for potassium hydroxide (KOH) bipolar stack systems. Though there is room for improvement on system energy efficiency, greater improvement is needed for the reduction of capital equipment costs with respect to volumes of produced hydrogen for these applications. One must also consider the durability of these systems, where PEM stacks are estimated to last 5 years, and KOH bipolar stacks are estimated to have a 7 year lifetime. In the NREL model, material costs such as KOH are insignificant relative to electricity and capital equipment.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

There is a need for energy efficient, low cost hydrogen generation systems which are amenable to high hydrogen flux. The systems, methods and devices described herein, each may have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of Certain Inventive Embodiments” one of ordinary skill in the art, informed by the disclosure herein, will understand how the features of this technology provide advantages that include durable electrochemical hydrogen generation. In particular, technology needs exist for durable electrochemical systems with a reduced number of sub-system operations and lower maintenance requirements. Resulting designs should be more cost effective per volume of produced hydrogen, more energy efficient, more durable and/or more reliable that current hydrogen generator technologies.

In a first aspect, an electrochemical cell for generation of hydrogen includes, for example, a cathode, a polymer electrolyte membrane surrounding the cathode and a housing surrounding the polymer electrolyte membrane.

In some embodiments, the housing comprises an anode and the anode is electrically connected to the cathode. In some embodiments, an anode compartment is formed between an anode side of the polymer electrolyte membrane and the housing. In some embodiments, the electrochemical cell further includes, for example, an inlet port in fluid communication with the anode compartment and configured to allow water flow into the anode compartment. In some embodiments, a cathode compartment is formed between a cathode side of the polymer electrolyte membrane and the cathode. In some embodiments, the cathode includes a first metal. In some embodiments, the first metal is selected from the group including Ni, nickel alloys, which may include, for example, Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti, or Zr. In some embodiments, the anode includes a second metal. In some embodiments, the second metal is selected from the group including austenitic stainless steels or duplex stainless steels, Ni or nickel alloys, wherein the nickel alloys further include Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti, Zr or alloys thereof. In some embodiments, the polymer electrolyte membrane is formed of perfluorinated ionomer, a copolymer of ethylene and a vinyl monomer containing an acid group or salts thereof, perfluorosulfonic acid/tetrafluoroethylene copolymers or perfluorocarboxylic acid/tetrafluoroethylene copolymer. In some embodiments, the electrochemical cell further includes, for example, a plurality of cathode-polymer electrolyte membrane structures within the housing.

In another aspect, a system for generation of hydrogen includes, for example, a water purifier in fluid communication with an electrochemical cell, an electrolyte source in fluid communication with the electrochemical cell and a power source electrically connected with the electrochemical cell.

In another aspect, a method of generating hydrogen includes, for example, providing an electrochemical cell, introducing water and hydroxide ions into the electrochemical cell, applying a voltage between the anode and the cathode and collecting hydrogen gas.

In a first aspect, an electrochemical cell for generation of hydrogen includes, for example, a cathode, a polymer electrolyte membrane surrounding the cathode, and a housing surrounding the polymer electrolyte membrane.

In some embodiments of the first aspect, the housing includes an anode. In some embodiments of the first aspect, the anode is electrically connected to the cathode. Some embodiments of the first aspect further include an anode compartment positioned between an anode side of the polymer electrolyte membrane and the housing. Some embodiments of the first aspect further include an inlet port in fluid communication with the anode compartment and configured to allow water flow into the anode compartment. In some embodiments of the first aspect, the cathode and the polymer electrolyte membrane surrounding the cathode includes a plurality of rod-shaped cathode-electrolyte membrane structures arranged in a radial configuration. In some embodiments of the first aspect, the polymer electrolyte membrane includes a first seal on a first end and a second seal on a second end. In some embodiments of the first aspect, the housing is configured to contain an electrolyte, and wherein the electrolyte includes hydroxide ions. In some embodiments of the first aspect, the electrolyte further includes aqueous halide salt. In some embodiments of the first aspect, the cathode includes a first metal. In some embodiments of the first aspect, the first metal is selected from the group consisting of nickel and nickel alloys of Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti or Zr. In some embodiments of the first aspect, the anode includes a second metal. In some embodiments of the first aspect, the second metal is selected from the group consisting of austenitic stainless steels, duplex stainless steels, nickel and nickel alloys of Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti or Zr. In some embodiments of the first aspect, the polymer electrolyte membrane is selected from the group consisting of a perfluorinated ionomer and a copolymer of ethylene and a vinyl monomer containing an acid group or salts thereof. In some embodiments of the first aspect, the perfluorinated ionomer is selected from the group consisting of perfluorosulfonic acid/tetrafluoroethylene copolymers and perfluorocarboxylic acid/tetrafluoroethylene copolymer. In some embodiments of the first aspect, the polymer electrolyte membrane includes an anionic exchange membrane. Some embodiments of the first aspect further include a plurality of cathode-polymer electrolyte membrane structures positioned within the housing. In some embodiments of the first aspect, the cathode is porous. In some embodiments of the first aspect, the cathode includes a cathode tube, and wherein the electrochemical cell further includes a cathode compartment including an interior space of the cathode tube. In some embodiments of the first aspect, the cathode is non-porous and wherein the electrochemical cell further includes a cathode compartment located between the cathode and the polymer electrolyte membrane.

In a second aspect, a system for generation of hydrogen includes, for example, a water purifier in fluid communication with an electrochemical cell of the first aspect, an electrolyte source in fluid communication with the electrochemical cell, and a power source electrically connected with the electrochemical cell.

In some embodiments of the second aspect, the electrochemical cell further includes an electrolyte circulation system configured to introduce, circulate and/or flush electrolyte solution from the electrochemical cell.

In a third aspect, a method of generating hydrogen includes, for example, introducing water and hydroxide ions into the electrochemical cell of the first aspect, applying a voltage between the anode and the cathode, and collecting hydrogen gas.

In some embodiments of the third aspect, the collected water saturated hydrogen gas has a purity greater than approximately 99.999 mol%. In some embodiments of the third aspect, the collected water saturated hydrogen gas has a purity greater than approximately 99.9999 mol%. In some embodiments of the third aspect, the cathode and the polymer electrolyte membrane surrounding the cathode includes a plurality of rod-shaped cathode-electrolyte membrane structures arranged in a radial configuration. In some embodiments of the third aspect, the hydrogen gas is collected at a pressure of from about 30 psig to about 60 psig. In some embodiments of the third aspect, the hydrogen gas is collected at a pressure of from about 200 psig to about 500 psig. In some embodiments of the third aspect, the hydrogen gas is collected at a pressure of from about 1000 psig to about 3000 psig. In some embodiments of the third aspect, the polymer electrolyte membrane includes a first seal on a first end and a second seal on a second end.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

FIG. 1 depicts a single radial oriented aqueous alkaline electrochemical cell in the form of a membrane tube assembly. Electrical leads are omitted for clarity.

FIG. 2 depicts a vertical cross section of an array of several cathode-electrolyte membrane assemblies.

FIG. 3 depicts a bundled array with several cathode-electrolyte membrane assemblies where the outer housing is omitted for clarity.

FIG. 4 depicts an electrochemical hydrogen generation system.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. The teachings herein can be applied in a multitude of different ways, including for example, as defined and covered by the claims. It should be apparent that the aspects herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative. Based on the teachings herein one skilled in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspect and that two or more of these aspects may be combined in various ways. For example, a system or apparatus may be implemented or a method may be practiced by one of skill in the art using any reasonable number or combination of the aspects set forth herein. In addition, such a system or apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure. It is to be understood that the disclosed embodiments are not limited to the examples described below, as other embodiments may fall within disclosure and the claims.

Some embodiments disclosed herein relate to an apparatus for generation of hydrogen. For example, FIG. 1 depicts one embodiment of an apparatus for generation of hydrogen. The apparatus includes a radial orientation, wherein an inner cathode is surrounded by a polymeric electrolyte membrane. In some embodiments, the inner cathode includes a directional seal through which product hydrogen may exit the apparatus. The inner cathode and the polymeric electrolyte membrane are contained within an outer housing. In some embodiments, the outer housing is configured to contain both apparatus components and aqueous solution within the apparatus.

In some embodiments, the inner cathode includes an inner cathode compartment formed of a porous metal membrane electrode. In some embodiments, the inner cathode electrode is constructed of a metal resistant to attack by hydroxide (OH⁺) ions in the presence of applied voltage. In some embodiments, the metal includes sintered Ni or other sintered nickel alloy. In some embodiments, the metal includes austenitic stainless steel, duplex stainless steel, Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti, Zr or other metals that may be configured to improve cathode efficiency for reduction of water to hydrogen gas and hydroxide ions. In some embodiments, the sintered metal membrane is configured to serve as the cathode as well as a porous passageway for product hydrogen gas to exit the apparatus. Porous metal membranes of this type are routinely used in the semiconductor industry as sintered metal filters or diffusers. Examples of porous metal membranes are available from Mott Corporation, Farmington, Conn., which membranes are formed of sintered Ni or sintered stainless steel with a porosity of from about 0.5 μm to about 100 μm.

A space between the inner cathode electrode and the polymer electrolyte membrane may contain, for example, potassium hydroxide or other Brönsted-Lowry base. This provides the primary electrolyte for the apparatus and facilitates water and hydroxide transfer across the polymeric electrolyte membrane. In some embodiments, the Brönsted-Lowry base includes Group I or Group II metal hydroxides. In some embodiments, the Brönsted-Lowry base includes a combination of Brönsted-Lowry bases. In some embodiments, the Brönsted-Lowry base is present in a concentration of less than about 0.1 moles/Liter. In some embodiments, the Brönsted-Lowry base is present in a concentration of from about 0.1 moles/Liter to about 5.0 moles/Liter.

In some embodiments, the electrolyte membrane includes materials that do not degrade when exposed to the Brönsted-Lowry base and an applied voltage. In some embodiments, the electrolyte membrane is formed of a perfluorinated ionomer. In some embodiments, the electrolyte membrane is formed of a copolymer of ethylene and a vinyl monomer containing an acid group or salts thereof. In some embodiments, the perfluorinated ionomer includes, but is not limited to, perfluorosulfonic acid/tetrafluoroethylene copolymers (“PFSA-TFE copolymer”) or perfluorocarboxylic acid/tetrafluoroethylene copolymer (“PFCA-TFE copolymer”). Some perfluorinated ionomers useful in embodiments of the present disclosure include commercially available NAFION® (E.I. du Pont de Nemours & Company), FLEMION® (Asahi Glass Company, Ltd), and ACIPLEX® (Asahi Chemical Industry Company). Some perfluorinated ionomers useful in embodiments of the present disclosure have a thickness of from about 1/32 inch to about ⅛ inch.

In some embodiments, the polymer ionomer membrane is in salt form, where protons have been replaced by metal or non-metal cations. In this form, the polymer membrane substituents contain anionic groups. In the case where potassium hydroxide is used as the primary electrolyte in the apparatus, the polymer ionomer membrane contains potassium cations (K⁺). In some embodiments, the polymer ionomer membrane may include, for example, an anion exchange membrane. Membranes of this type are known for rapid anion exchange and transport properties which encompass hydroxide (OH⁻) ions. The ionic polymer membrane also may be configured to serve as a gas separator and water transfer agent and an additional electrolyte. In some embodiments, the ionic polymer membrane is a Nafion® membrane made by DuPont™. It is a cationic exchange membrane. In some embodiments, in which an anionic exchange membrane is used, the cation is incorporated into the polymer and the anion is floating around. These are typically non-coordinating anions. Commercially available ionomer membranes may be obtained, for example, from Rohm and Haas Company, E.I. du Pont de Nemours & Company and/or Dow Chemical Company.

The inner portion of the polymeric membrane is generally positioned in close proximity to the inner cathode electrode. In some embodiments, the inner portion of the polymeric membrane contacts the cathode electrode. As mentioned above, in some embodiments the cathode is formed of a porous metal or of fused metal particles or of a sintered metal where many small particles are fused together with spaces between. The pores or spaces between the metal particles are generally of a diameter from about 0.1 μm to about 100 μm. The diameter of the cathode is preferably from about 1/16 to about ½ inch. In some embodiments, the cathode is formed in a tube-like structure. In other embodiments, the cathode is formed in a rod-shaped or helical shaped structure.

In operation, as soon as hydroxide ions migrate across the polymer membrane, hydroxide ions contact the sintered metal. In the presence of the applied voltage the hydroxide ions combine to become water and hydrogen gas. This process is described more fully below with regard to systems and methods of generating hydrogen. Thus, fitting the polymer membrane around a porous sintered metal tube structure with as close contact as possible can reduce distance an ion has to travel, and thus, increase productivity of the apparatus.

The porous metal cathode may be connected to a solid tube, which serves as an outlet for hydrogen to exit the cell via a directional seal. The directional seal is a one-way pre-loaded seal. It can be a spring loaded or weighted to have a pressure on the seal so it is configured to open only at a specific pressure. In some embodiments, the directional seal is similar to a pressure release valve. Mechanical means may be used to open the directional seal in a single direction at a specific force—to release pressure from a high pressure region to a low pressure region. Some types of directional seals useful for embodiments of the present disclosure can be purchased from Swagelok™ or Valin™.

As illustrated in FIG. 1, the outer housing comprises an outer anode shell. In some embodiments, the anode shell is formed of a metal. In some embodiments, the metal is configured to be resistant to attack by hydroxide (OH⁻) ions in the presence of applied voltage. In some embodiments, the metal is configured to improve anode efficiency for oxidation of hydroxide ions to oxygen gas and water. The metal may include Ni or nickel alloys. In some embodiments, the metal includes, austenitic stainless steels, duplex stainless steels, Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti, Zr, alloys of any of these metals or some combination thereof. In some embodiments, the anode shell is formed of a conductive polymer. In some embodiments, the outer housing is formed of a non-metal material, such as plastic.

The anode is electrically connected to the cathode through an electrical wire or other suitable electrically conductive material. Electrical conducting material may include, for example, a wire, trace, conducting member, etc. In operation, a voltage may be applied across the electrical conducting material from about −1.0 V to about −3.5 V. At the applied voltage, water reacts at the cathode to form H₂ gas and to reform hydroxide ions (OH⁻).

The embodiment of the apparatus depicted in FIG. 1 is an aqueous alkaline electrochemical cell. Thus, the base of the apparatus includes an inlet configured for water entering the outer housing and the top of the apparatus includes an outlet configured for oxygen gas generated during operation of the apparatus to exit the outer housing. During operation, build up of excess oxygen gas may occur on the anode side of the membrane. This gas can be periodically or continuously vented through an outlet port. The outlet for oxygen gas may include a pressure sensitive valve or transducer. The pressure sensitive valve or transducer may be configured to allow oxygen gas to be released at specific pressures. As discussed further below, the oxygen gas may be released based upon the pressure of the product hydrogen on the other side of the polymeric membrane. Additionally, the inner cathode includes an outlet for hydrogen gas generated during operation of the apparatus.

In some embodiments, the water flowing into the apparatus via the inlet is pre-purified in a water purifier as described further below with regard to FIG. 4.

As noted above, the outer housing may be configured to contain aqueous hydroxide ion (OH⁻). In some embodiments, the outer housing is configured to contain an aqueous inorganic salt mixed with hydroxide ions. The space between the polymer membrane and the outer housing may include, for example, potassium hydroxide or other Brönsted-Lowry bases. In some embodiments, the outer housing is configured to contain an aqueous halide salt mixed with hydroxide ions. This provides the primary electrolyte to facilitate oxidation of hydroxide ion to water and O₂ gas.

The build up of oxygen gas pressure can be advantageous when producing high pressure hydrogen gas product. Further, in certain instances it may be advantageous to allow oxygen gas pressure build-up in the anode compartment to facilitate water transport across the polymeric membrane. The radial design of the electrochemical cell is configured to allow continuous maintenance of high operating pressures with inner components, (such as the polymer electrolyte membrane), which are not required to have the same thickness as the outer wall. Pressure build-up of product hydrogen can be balanced with oxygen pressure in the anode compartment. Differential pressure across the membrane separator (polymer electrolyte membrane) is reduced or even minimized and high pressure on the outer wall of up to about 10,000 psig can be achieved. In certain embodiments, the differential pressure between the anode side of the polymer electrolyte membrane and the cathode side of the polymer electrolyte membrane is approximately 5 psig or less. In other words, pressure at center cathode is approximately the same as pressure on the outer housing so the polymer electrolyte membrane does not collapse.

Generally, instrumentation included in the apparatus depicted in FIG. 1 is operated at pressures of from about 30 psig to about 750 psig, but may be operated at pressures up to about 3000 psig. In some embodiments, the apparatus depicted in FIG. 1 is operated at pressures of up to and including about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1250, 1500, 1750, 2000, 2250, 2500, 2750, 3000, 3250, 3500, 3750, 4000, 4250, 4500, 4750, 5000 psig or any number in between. The apparatus is configured to be sealed in a manner that separates inlet gases from outlet gases and only allows for water and hydroxide (OFF) transport through the membrane. For use at pressures above 750 psig, for example, from about 1000 psig to about 3000 psig the outer housing may be formed with a thickness of from about ½ to about 1 inch stainless steel. The anode electrode may be formed of an insert or a sleeve to line the inside of the outer housing. The insert or sleeve may be configured to provide support to the outer housing.

In some embodiments, the electrochemical hydrogen generation device includes, for example, a bundled array of cathode-electrolyte membrane assemblies positioned substantially parallel with respect to each other. FIG. 2 depicts a vertical cross section of an array of several cathode-electrolyte membrane assemblies. Electrical leads are omitted for clarity. FIG. 3 depicts a bundled array with several cathode-electrolyte membrane assemblies where the outer housing is omitted for clarity. These types of designs can maximize hydrogen generation in a nominal amount of space. Each bundled array of cathode-electrolyte membrane assemblies increases surface area, and thus, is configured to have a small system footprint. In some embodiments, a bundle includes, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 24, 32, 40, 48, 56, 64 or more cathode-electrolyte membrane assemblies. In some embodiments, a bundle includes 8 cathode-electrolyte membrane assemblies. In some embodiments, a bundle includes 16 cathode-electrolyte membrane assemblies. In some embodiments, end caps on each cathode-electrolyte membrane assembly are each from about 2 inches to about 3 inches in diameter.

The radial design of the electrochemical cells depicted in FIG. 1 coupled with the membrane bundles depicted in FIGS. 2 and 3 are configured to allow for a maximum output of hydrogen production with a minimal amount of space. Current devices and systems known in the art for producing hydrogen rely on bipolar plates, which cannot be configured for efficient high throughput production of hydrogen.

Some embodiments disclosed herein relate to systems for generation of hydrogen. FIG. 4 depicts an electrochemical hydrogen generating system. In the system of FIG. 4, process water passes through a water purifier. The water purifier may be configured to remove contaminants from the process water that could corrode or otherwise contaminate electrodes. For example, the water purifier may be configured to remove sulfur or phosphorus or CO₂ from the process water.

The water purifier is in fluid communication with a feed water storage tank. The high purity water exiting the water purifier may then be stored in the feed water storage tank for later use in generation of hydrogen. The feed water storage tank may be formed of materials configured to prevent introduction of contaminants into the high purity water. The materials may include, for example, high purity plastics, stainless steel, Ni or Ni alloy, and/or quartz. In some embodiments, the water purifier or the feed water storage tank may include, for example, a mechanical pump configured to deliver the high purity water under pressure to the hydrogen generation unit.

In some embodiments, an electrolyte mixing tank is placed upstream of and in fluid communication with the hydrogen generation unit. Illustrated in FIG. 4 is a type of electrolyte mixing tank, a KOH mixing tank. Although the KOH making tank holds aqueous potassium hydroxide, it will be understood by one of ordinary skill in the art, that any suitable aqueous inorganic salt, including, for example, aqueous halide/hydroxide salt mixtures can be made and used in the system. In some embodiments, the resulting electrolyte solution from the KOH mixing tank is provided together with the high purity water flowing from the feed water storage tank. The resulting mixture of electrolyte solution and high purity water then flows into the hydrogen generation unit. In other embodiments, the hydrogen generation unit contains addition ports where controlled amounts of electrolyte and water may be introduced and subsequently mixed to form a dissolved electrolyte solution. In some embodiments, a concentration gradient may exist in the mixed electrolyte solution.

The hydrogen generation unit is electrically connected to a power supply. In some embodiments, the power source includes an electrical outlet attached to a grid or an electrochemical battery with stored energy. In some embodiments, the power source includes a sustainable energy such as solar, wind or hydroelectric power. In some embodiments, the hydrogen generation unit is electrically connected to a power supply by a wire, trace, conducting member or the like. In some embodiments, the wire is formed of Ni, Cu or Au. In some embodiments, the wire includes electrical leads formed of Ni or Ni alloys such as Ni-Al or Ni-Zn. In some embodiments, the electrical wires are positioned on the outside of the electrochemical cell apparatus and thus do not contact corrosive materials. In some embodiments, a voltmeter or potentiometer is electrically connected to the electrical wire.

In some embodiments, the hydrogen generation unit includes an aqueous alkaline electrochemical cell with a radial orientation. In some embodiments, the hydrogen generation unit may include, for example, an apparatus depicted in at least one of FIGS. 1-3.

In the embodiment of FIG. 4, the hydrogen generation unit includes an electrolysis module, an electrolyte circulation and a hydrogen gas dryer/purifier. In some embodiments, the hydrogen generation unit includes a metal membrane hydrogen purifier. In some embodiments, the hydrogen generation unit includes a hydrogen purifier containing metal in a reduced oxidation state. In some embodiments, the hydrogen generation unit includes an electrolyte circulation system. The electrolyte circulation system may be configured to introduce, circulate and/or flush electrolyte solution from the hydrogen generation apparatus.

The hydrogen generation unit illustrated in FIG. 4 is in fluid communication with a compressor. In operation, greater than 99% pure hydrogen generated in the hydrogen generation unit may flow from the hydrogen generation unit into the compressor. The compressor specifications are defined by intended hydrogen usage, where compression up to about 3000 psig may be used. In some embodiments, compression up to about 3250, 3500, 3750, 4000, 4250, 4500, 4750, 5000, 6000, 7000, 8000, 9000, 10,000 psig or any number in between may be used. In some embodiments, the compressor is formed of explosion proof, high purity materials. In some embodiments, the compressor is free of oil or grease. In some embodiments the compressor includes high purity seals. In some embodiments, the high purity seals are formed of Teflon or other high elastomeric materials. In some embodiments, the high purity seals include metal to metal seals. As further illustrated in FIG. 4, the hydrogen compressor is in fluid communication with a hydrogen storage unit. In operation, the hydrogen compressed in the compressor may be delivered to the hydrogen storage unit for storage until use. In some embodiments, the storage vessel is constructed of materials to prevent contamination of product hydrogen. In some embodiments, the materials include, for example, high purity plastics, stainless steel, Ni or Ni alloys. In general, the hydrogen storage units for storing high pressure hydrogen (up to about 10,000 psig) are formed of stainless steel.

Some embodiments disclosed herein relate to methods of electrochemical generation of hydrogen. In one embodiment, a method includes, for example, providing aqueous hydroxide ion (OH⁻) within an outer anode compartment bounded by a first side of an electrolyte membrane and a housing comprising an anode, providing a cathode on a second side of the electrolyte membrane, and providing a voltage potential between the anode and the cathode so water reacts at the cathode to form H₂ gas and to reform hydroxide ions, so hydroxide ions migrate from the cathode side of the electrolyte membrane to the anode side of the electrolyte membrane and so water and oxygen gas are generated in the anode compartment.

In some embodiments, water is pre-purified prior to introduction to the electrochemical hydrogen generator. In some embodiments, the water is purified using ion exchange resins. In some embodiments, the water is purified using reverse osmosis. In some embodiments, the water is purified using distillation. In some embodiments, the water is purified to remove materials that would otherwise contaminate electrodes in the apparatus. In some embodiments, the water is purified to remove sulfur. In some embodiments, the water is purified to remove phosphorus. In some embodiments, the water is purified to remove CO₂ or other gaseous contaminants. Gaseous contaminants may include nitrogen, oxygen or CO. In some embodiments, the water is purified to remove metal containing species, silica, silicates, acids, halogen containing species, refractory compounds and/or organic compounds. In some embodiments, acceptable contaminant levels following purification are less than about 1 ppm. In some embodiments, acceptable contaminant levels following purification are less than about 1 ppb. In some embodiments, acceptable contaminant levels following purification are less than about 1 ppt.

Water is provided to the anode and/or cathode compartment to replenish water consumed during operation of the electrochemical cell. In some embodiments, the water is periodically added to the anode or cathode compartment through an inlet port. In some embodiments, the water is continuously added to the anode or cathode compartment through an inlet port. The water flowing through the inlet port is subsequently converted to hydrogen and oxygen by the electrochemical cell. In some embodiments, a water purifier or a feed water storage tank mechanically increases the pressure of the high purity water. The high purity water may be delivered from either the water purifier or the feed water storage tank to the hydrogen generation unit. In some embodiments, the water flows into the apparatus from the water purifier. The water in the purifier may be degassed prior to introduction into the hydrogen generating apparatus. Water may be delivered to the apparatus at pressure to facilitate production of high pressure product hydrogen. In some embodiments, water is delivered at up to approximately 100 psig. Water may be delivered at up to approximately 50,60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 psig or any number in between.

In some embodiments, water and electrolyte are circulated continuously through the anode and cathode compartments to aid in removing gas bubbles and/or to prevent dry spots from forming on the membrane surface. Ultrasound may be used to remove gas bubbles and/or to prevent dry spots from forming on the membrane surface. In some embodiments, water and electrolyte are flushed out of the anode and cathode compartments to remove unwanted residues, scales or soluble contaminants. These solutions may be replaced with fresh water and/or electrolyte solution. Depending on the purity of the inlet water, flushing may be infrequent.

Oxygen gas may be released from the apparatus at specific pressures by a pressure sensitive valve. During operation of the electrochemical cell, the pressure of the oxygen gas remains roughly equivalent to the pressure of the product hydrogen. The pressure of the product hydrogen and the pressure of the oxygen may be maintained at from about 60 psig to about 3000 psig. In some embodiments, the pressure of the oxygen and the product hydrogen is maintained at from about 300 psig to about 500 psig. In some embodiments, oxygen pressure on the anode side of the electrolyte membrane is allowed to build up in a controlled fashion to balance pressure build up of product hydrogen on the cathode side of the electrolyte membrane. In some embodiments, oxygen pressure is within approximately 5 psig of hydrogen pressure. In some embodiments, oxygen pressure is equal to hydrogen pressure.

In some embodiments, product hydrogen may exit out of the cathode compartment through a solid tube which is mechanically connected to the porous metal cathode. The solid tube fluidly connects to a directional seal which is configured to allow the product hydrogen to exit the hydrogen generating apparatus. The product hydrogen may be delivered at a pressure of from about 30 psig to about 60 psig. The product hydrogen may be delivered at a pressure of from about 200 psig to about 500 psig. The product hydrogen may be delivered at a pressure of from about 1000 psig to about 3000 psig. In some embodiments, the product hydrogen is delivered at a pressure of up to about 10,000 psig. In some embodiments, the hydrogen gas is produced at high pressure and then stored at high pressure. In some embodiments the hydrogen gas is produced at lower pressure, and then, mechanical means are used to compress the product hydrogen to higher pressure for storage.

The product hydrogen may be compressed by mechanical or other methods after exiting the apparatus. In some embodiments, product hydrogen is directed from the electrochemical cell to a hydrogen drier or a purification unit. In some embodiments, the hydrogen drier may include, for example, a polymer membrane dehumidification device. In some embodiments, the hydrogen drier includes, for example, molecular sieves, silica, alumina, zeolites, or other water adsorbing materials.

In some embodiments, the purity of the product hydrogen is approximately 99.999 mol% or more. In some embodiments, the purity of the product hydrogen is approximately 99.9999 mol% or more. In some embodiments, the purity of the product hydrogen is approximately 99.99999 mol% or more. Water vapor may be removed from the product hydrogen with a membrane drying device level of less than 10 ppm. Water vapor may be removed from the product hydrogen with an adsorbent-based drier to a level of less than 100 ppb. In some embodiments, gaseous contaminants are removed from the product hydrogen with a gas purifier to give a total contaminant level of less than 100 ppb.

In some embodiments, oxygen by-product exits out of a gas port in fluid communication with the outer anode compartment. The purity of the oxygen by-product may be approximately 99.9999 mol% or more. In some embodiments, the oxygen gas is vented to air. In some embodiments, the oxygen gas is collected for subsequent use.

The product hydrogen may contain less than about 1% water vapor. The product hydrogen may contain from about 1% to about 0.1% water vapor. The product hydrogen may contain from about 0.1% to about 1 ppm water vapor. The product hydrogen may contain less than about 1 ppm water vapor. The product hydrogen may contain less than about 1 ppb water vapor.

In the case that water vapor needs to be removed from the product hydrogen for high purity applications, several known methods of moisture removal from hydrogen are readily available. For example, water vapor can be removed through use of at least one of a molecular sieve, a membrane dryer from RASIRC™, or a membrane dryer from Perma Pure, LLC.

All references cited herein are incorporated herein by reference in their entireties. To the extent publications and patents or patent applications incorporated by reference contradict the disclosure contained in the specification, the specification is intended to supersede and/or take precedence over any such contradictory material.

Unless otherwise defined, all terms (including technical and scientific terms) are to be given their ordinary and customary meaning to a person of ordinary skill in the art, and are not to be limited to a special or customized meaning unless expressly so defined herein.

Terms and phrases used in this application, and variations thereof, especially in the appended claims, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing, the term ‘including’ should be read to mean ‘including, without limitation,’ ‘including but not limited to,’ or the like; the term ‘comprising’ as used herein is synonymous with ‘including,’ ‘containing,’ or ‘characterized by,’ and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps; the term ‘having’ should be interpreted as ‘having at least;’ the term ‘includes’ should be interpreted as ‘includes but is not limited to;’ the term ‘example’ is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; adjectives such as ‘known’, ‘normal’, ‘standard’, and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass known, normal, or standard technologies that may be available or known now or at any time in the future; and use of terms like ‘preferably,’ ‘preferred,’ ‘desired,’ or ‘desirable,’ and words of similar meaning should not be understood as implying that certain features are critical, essential, or even important to the structure or function of the invention, but instead as merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the invention. Likewise, a group of items linked with the conjunction ‘and’ should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as ‘and/of’ unless expressly stated otherwise. Similarly, a group of items linked with the conjunction ‘or’ should not be read as requiring mutual exclusivity among that group, but rather should be read as ‘and/of’ unless expressly stated otherwise.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

All numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification are to be understood as being modified in all instances by the term ‘about.’ Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of any claims in any application claiming priority to the present application, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

Furthermore, although the foregoing has been described in some detail by way of illustrations and examples for purposes of clarity and understanding, it is apparent to those skilled in the art that certain changes and modifications may be practiced. Therefore, the description and examples should not be construed as limiting the scope of the invention to the specific embodiments and examples described herein, but rather to also cover all modification and alternatives coming with the true scope and spirit of the invention.

Claims

1. An electrochemical cell for generation of hydrogen, comprising:

a cathode;

a polymer electrolyte membrane surrounding the cathode; and

a housing surrounding the polymer electrolyte membrane, wherein the housing comprises an anode, and wherein the anode is electrically connected to the cathode.

2. The electrochemical cell of claim 1, comprising an anode compartment positioned between an anode side of the polymer electrolyte membrane and the housing.

3. The electrochemical cell of claim 2 further comprising an inlet port in fluid communication with the anode compartment and configured to allow water flow into the anode compartment.

4. The electrochemical cell of claim 1, wherein the cathode and the polymer electrolyte membrane surrounding the cathode comprises a plurality of rod-shaped cathode-electrolyte membrane structures arranged in a radial configuration.

5. The electrochemical cell of claim 4, wherein the polymer electrolyte membrane comprises a first seal on a first end and a second seal on a second end.

6. The electrochemical cell of claim 1, wherein the housing is configured to contain an electrolyte, and wherein the electrolyte comprises hydroxide ions.

7. The electrochemical cell of claim 6, wherein the electrolyte further comprises aqueous halide salt.

8. The electrochemical cell of claim 1, wherein the cathode comprises a first metal.

9. The electrochemical cell of claim 8, wherein the first metal is selected from the group consisting of nickel and nickel alloys of Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti or Zr.

10. The electrochemical cell of claim 1, wherein the anode comprises a second metal.

11. The electrochemical cell of claim 10, wherein the second metal is selected from the group consisting of austenitic stainless steels, duplex stainless steels, nickel and nickel alloys of Pt, Pd, Cr, Mo, Fe, Ta, Ru, Rh, W, Os, Ir, Zn, Co, Ti or Zr.

12. The electrochemical cell of claim 1, wherein the polymer electrolyte membrane is selected from the group consisting of a perfluorinated ionomer and a copolymer of ethylene and a vinyl monomer containing an acid group or salts thereof

13. The electrochemical cell of claim 12, wherein the perfluorinated ionomer is selected from the group consisting of perfluorosulfonic acid/tetrafluoroethylene copolymers and perfluorocarboxylic acid/tetrafluoroethylene copolymer.

14. The electrochemical cell of claim 1, wherein the polymer electrolyte membrane comprises an anionic exchange membrane.

15. The electrochemical cell of claim 1 further comprising a plurality of cathode-polymer electrolyte membrane structures positioned within the housing.

16. The electrochemical cell of claim 1, wherein the cathode is porous, wherein the cathode comprises a cathode tube, and wherein the electrochemical cell further includes a cathode compartment including an interior space of the cathode tube.

17. The electrochemical cell of claim 1, wherein the cathode is non-porous and wherein the electrochemical cell further comprises a cathode compartment located between the cathode and the polymer electrolyte membrane.

18. A system for generation of hydrogen, comprising:

a water purifier in fluid communication with an electrochemical cell of claim 1;

an electrolyte source in fluid communication with the electrochemical cell; and

a power source electrically connected with the electrochemical cell.

19. The system of claim 18, wherein the electrochemical cell further comprises an electrolyte circulation system configured to introduce, circulate and/or flush electrolyte solution from the electrochemical cell.

20. A method of generating hydrogen, comprising:

introducing water and hydroxide ions into the electrochemical cell of claim 1;

applying a voltage between the anode and the cathode; and

collecting hydrogen gas.

21. The method of claim 20, wherein the collected water saturated hydrogen gas has a purity greater than approximately 99.999 mol%.

22. The method of claim 20, wherein the collected water saturated hydrogen gas has a purity has a purity greater than approximately 99.9999 mol%.

23. The method of claim 20, wherein the cathode and the polymer electrolyte membrane surrounding the cathode comprises one or more rod-shaped cathode-electrolyte membrane structures arranged in a radial configuration, wherein the hydrogen gas is collected at a pressure of from about 30 psig to about 60 psig, and wherein the polymer electrolyte membrane comprises a first seal on a first end and a second seal on a second end.

24. The method of claim 20, wherein the cathode and the polymer electrolyte membrane surrounding the cathode comprises one or more rod-shaped cathode-electrolyte membrane structures arranged in a radial configuration, wherein the hydrogen gas is collected at a pressure of from about 200 psig to about 500 psig, and wherein the polymer electrolyte membrane comprises a first seal on a first end and a second seal on a second end.

25. The method of claim 20, wherein the cathode and the polymer electrolyte membrane surrounding the cathode comprises one or more rod-shaped cathode-electrolyte membrane structures arranged in a radial configuration, wherein the hydrogen gas is collected at a pressure of from about 1000 psig to about 3000 psig, and wherein the polymer electrolyte membrane comprises a first seal on a first end and a second seal on a second end.