Electrochemical hydrogen production by ammonia decomposition

Abstract

Contemplated herein is a method for producing hydrogen comprising: (a) providing an electrochemical reactor having an anode, a cathode, and a membrane between the anode and the cathode, wherein the membrane conducts both electrons and protons, and wherein the anode and the cathode are porous; (b) introducing a first stream comprising ammonia or decomposed ammonia products to the anode; and (c) extracting a second stream comprising hydrogen from the cathode, wherein the first stream and the second stream are separated by the membrane.

Description

[Technical Field]

[0001] The present invention relates generally to hydrogen production. More specifically, the present invention relates to electrochemical hydrogen production using ammonia. [Background technology]

[0002] The petroleum and chemical industries require large amounts of hydrogen. For example, large amounts are used to upgrade fossil fuels and produce methanol or hydrochloric acid. Petrochemical plants require hydrogen for hydrocracking, hydrodesulfurization, and hydrodealkylation. Hydrogen is also required for hydrogenation processes to increase the saturation level of unsaturated fats and oils. Hydrogen is also a reducing agent for metal ores. Hydrogen can be produced by water electrolysis, steam reforming, laboratory-scale metal-acid processes, thermochemical methods, or anaerobic corrosion. Many countries are moving toward a hydrogen economy, but this requires the transportation of large amounts of hydrogen. Ammonia has been recognized as a suitable alternative molecule for hydrogen transportation because it is relatively easy to contain and transport compared to pressurized or liquefied hydrogen. However, ammonia is not easily utilized on its own and must be converted into hydrogen. Unfortunately, during this conversion process, hydrogen is produced and mixed with nitrogen, and the two gases cannot be separated easily, efficiently, or economically. To utilize ammonia in conventional systems and processes, the hydrogen must be separated from the nitrogen.

[0003] Clearly, there is a growing need and interest in developing new technology platforms for producing hydrogen. This disclosure discusses the generation of hydrogen using ammonia via an efficient electrochemical route. Electrochemical reactors and methods for carrying out such reactions are discussed. Summary of the Invention

[0004] Contemplated herein is a method for producing hydrogen comprising: (a) providing an electrochemical reactor having an anode, a cathode, and a membrane between the anode and the cathode, wherein the membrane conducts both electrons and protons, and wherein the anode and the cathode are porous; (b) introducing a first stream comprising ammonia or decomposed ammonia products to the anode; and (c) extracting a second stream comprising hydrogen from the cathode, wherein the first stream and the second stream are separated by the membrane.

[0005] In one embodiment, the ammonia decomposition occurs in situ at the anode. In one embodiment, the method includes applying a vacuum to the cathode. In one embodiment, the membrane, anode, and cathode have the same elements.

[0006] In one embodiment, the membrane, anode, and cathode comprise a proton-conducting phase and an electron-conducting phase. In one embodiment, the proton-conducting phase is BaHf x Ce 0.8-x Y 0.1 Yb 0.1 O 3-δ (BHCYYb), BaZr x Ce 0.8-x Y 0.1 Yb 0.1 O 3-δ (BZCYYb), yttrium-doped barium zirconate, yttrium-doped barium zirconate cerate, barium zirconate cerate, or a combination thereof. In one embodiment, the electronically conductive phase comprises doped lanthanum chromite, lanthanum-doped strontium titanate (LST), an electronically conductive metal, or a combination thereof.

[0007] In one embodiment, the LST comprises LaSrCaTiO. In one embodiment, the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof. In one embodiment, the doped lanthanum chromite comprises strontium-doped lanthanum chromite, iron-doped lanthanum chromite, strontium- and iron-doped lanthanum chromite, lanthanum calcium chromite, or a combination thereof.

[0008] In one embodiment, the hydrogen partial pressure at the anode is higher than the hydrogen partial pressure at the cathode.In one embodiment, the method includes introducing steam to the cathode.

[0009] Also contemplated herein is a hydrogen production system comprising: an ammonia source or a cracked ammonia product source; and an electrochemical (EC) reactor comprising an anode, a cathode, and a membrane between the anode and the cathode, the membrane conducting both electrons and protons, wherein the anode and the cathode are porous, and the EC reactor is configured to receive a first stream from the ammonia source or the cracked ammonia product source at the anode side, and the EC reactor is configured to output a second stream at the cathode side, the second stream comprising hydrogen.

[0010] In one embodiment, the reactor does not include an interconnect and does not include a current collector. In one embodiment, the anode, cathode, and membrane have the same elements. In one embodiment, the anode, cathode, and membrane include a proton-conducting phase and an electron-conducting phase. In one embodiment, the proton-conducting phase is BaHf x Ce 0.8-x Y 0.1 Yb 0.1 O 3-δ (BHCYYb), BaZr x Ce 0.8-x Y 0.1 Yb 0.1 O 3-δ(BZCYYb), yttrium-doped barium zirconate, yttrium-doped barium zirconate cerate, barium zirconate cerate, or a combination thereof.

[0011] In one embodiment, the electronically conductive phase comprises doped lanthanum chromite, lanthanum-doped strontium titanate (LST), an electronically conductive metal, or a combination thereof. In one embodiment, the LST comprises LaSrCaTiO. In one embodiment, the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof. In one embodiment, the doped lanthanum chromite comprises strontium-doped lanthanum chromite, iron-doped lanthanum chromite, strontium- and iron-doped lanthanum chromite, lanthanum calcium chromite, or a combination thereof.

[0012] In one embodiment, the cathode is configured to receive a vacuum. In one embodiment, the first stream and the second stream are separated by a membrane. In one embodiment, the reactor is configured to operate at a temperature of 500°C or greater. In one embodiment, the hydrogen partial pressure at the anode is greater than the hydrogen partial pressure at the cathode. In one embodiment, the cathode is also configured to receive steam.

[0013] Further aspects and embodiments are provided in the following drawings, detailed description, and claims. Unless otherwise specified, features described herein may be combined, and all such combinations are within the scope of the present disclosure.

[0014] The following drawings are provided to illustrate certain embodiments described herein. The drawings are merely illustrative and are not intended to limit the scope of the claimed invention, nor are they intended to show every possible feature or embodiment of the claimed invention. The drawings are not necessarily drawn to scale, and in some instances, certain elements of the drawings may be enlarged relative to other elements of the drawings for illustrative purposes. [Brief explanation of the drawings]

[0015] [Figure 1] 1 illustrates an electrochemical (EC) reactor according to one embodiment of the present disclosure. [Figure 2A] 1 illustrates a tubular electrochemical reactor according to one embodiment of the present disclosure. [Figure 2B] 1 illustrates a cross section of a tubular electrochemical reactor according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] overview Ammonia is an abundant and common chemical that can be transported worldwide. Furthermore, ammonia does not require high pressure or cryogenic storage (unlike hydrogen) and has an energy density ten times greater than that of lithium-ion batteries. Thus, using ammonia to produce hydrogen would be highly advantageous if it could be done efficiently and economically. This disclosure discusses electrochemical systems and methods suitable for producing hydrogen using ammonia.

[0017] The following terms and phrases have the meanings set forth below unless otherwise specified herein. This disclosure may employ other terms and phrases not expressly defined herein. Such other terms and phrases shall have the meanings that one of ordinary skill in the art would have within the context of this disclosure. In some cases, terms or phrases may be defined in the singular or plural. In such cases, it is understood that singular terms may also include the plural, and vice versa, unless specifically stated to the contrary.

[0018] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, reference to a "substituent" includes a single substituent as well as two or more substituents, etc. As used herein, "for example," "for instance," "such as," or "including" means introducing an example that further clarifies a more general subject matter. Unless otherwise expressly stated, such examples are provided merely as an aid in understanding the embodiments illustrated in this disclosure and are not intended to be limiting in any way. Furthermore, these terms do not imply any preference of any kind over the disclosed embodiments.

[0019] As used herein, unless otherwise specified, composition and material are used interchangeably. Each composition / material may have multiple elements, phases, and constituents. Heating, as used herein, refers to the active application of energy to a composition or material.

[0020] As used herein, YSZ refers to yttria-stabilized zirconia, SDC refers to samaria-doped ceria, SSZ refers to scandia-stabilized zirconia, and LSGM refers to lanthanum strontium gallate magnesite.

[0021] In this disclosure, the absence of substantial amounts of H2 means that the volumetric hydrogen content is 5% or less, or 3% or less, or 2% or less, or 1% or less, or 0.5% or less, or 0.1% or less, or 0.05% or less.

[0022] As used herein, CGO refers to gadolinium-doped ceria, which is also known as gadolinia-doped ceria, gadolinium-doped cerium oxide, cerium(IV) oxide, gadolinium-doped, GDC, or GCO (formula Gd:CeO). CGO and GDC are used interchangeably unless otherwise specified. Syngas (i.e., synthesis gas) in this disclosure refers to a mixture consisting primarily of hydrogen, carbon monoxide, and carbon dioxide.

[0023] Mixed conducting membranes can transport both electrons and ions. Ionic conductivity includes ionic species such as oxygen ions (or oxide ions), protons, halide anions, chalcogenide anions, etc. In various embodiments, the mixed conducting membranes of the present disclosure include an electronically conducting phase and an ionically conducting phase.

[0024] In this disclosure, the axial cross section of the tubular body is shown as being circular, but this is by way of example only and not limitation, and the axial cross section of the tubular body may be any suitable shape known to those skilled in the art, such as a square, a rounded square, a rectangle, a rounded rectangle, a triangle, a hexagon, a pentagon, an ellipse, an irregular shape, etc.

[0025] As used herein, ceria refers to cerium oxide, also known as cerium oxide, cerium dioxide, or cerium dioxide, which is an oxide of the rare earth metal cerium. Doped ceria refers to ceria doped with other elements, such as samaria-doped ceria (SDC) or gadolinium-doped ceria (GDC or CGO). As used herein, chromite refers to chromium oxide, including all oxidation states of chromium oxide.

[0026] As used herein, an impermeable layer or material refers to being impermeable to fluid flow, for example, an impermeable layer or material has a permeability of less than 1 microdarcy, or less than 1 nanodarcy.

[0027] In this disclosure, sintering refers to a process of forming a solid mass of material by heat or pressure, or a combination thereof, without melting the material to the point of liquidity. For example, particles of a material are heated to agglomerate into a solid or porous mass, causing atoms within the material particles to diffuse across the particle boundaries and fuse the particles to form one solid piece.

[0028] The term "in situ" in this disclosure refers to a processing (e.g., heating or decomposition) step occurring in the same place or in the same equipment. For example, ammonia decomposition occurring at the anode in an electrochemical reactor is considered in situ.

[0029] Electrochemistry is the branch of physical chemistry concerned with the relationship between electric potential as a measurable and quantitative phenomenon and the electric potential resulting from a specific chemical change, or vice versa. These reactions involve electrons moving between electrodes through electronically conducting phases (typically, but not necessarily, an external electric circuit) separated by an ionically conducting, electronically insulating membrane (or ionic species in solution). When a chemical reaction is influenced by a potential difference, as in electrolysis, or when an electric potential arises from a chemical reaction, as in a battery or fuel cell, it is called an electrochemical reaction. Unlike chemical reactions, in electrochemical reactions, electrons (and the resulting ions) are transferred not directly between molecules but through the electronically and ionically conducting circuits, respectively. This phenomenon distinguishes electrochemical reactions from chemical reactions.

[0030] In connection with electrochemical reactors and methods of use thereof, various components of the reactor, such as electrodes and membranes, are described, along with the materials of construction of the components. The following description lists various aspects and embodiments of the invention disclosed herein. The specific embodiments are not intended to define the scope of the invention. Rather, the embodiments provide non-limiting examples of various compositions and methods that fall within the scope of the claimed invention. This description should be read from the perspective of one of ordinary skill in the art. As such, it does not necessarily include information that is known to one of ordinary skill in the art.

[0031] Interconnects in electrochemical devices (e.g., fuel cells) are often made of metal or ceramic and are placed between individual cells or repeating units. Their purpose is to connect each cell or repeating unit so that electricity can be distributed or combined. Interconnects are also called bipolar plates in electrochemical devices. As used herein, an impermeable layer interconnect refers to an interconnect that is a layer that is impermeable to fluid flow. Electrochemical Reactor

[0032] FIG. 1 illustrates an electrochemical (EC) reactor 100 according to one embodiment of the present disclosure. The EC reactor 100 includes a first electrode 101, a membrane 103, and a second electrode 102. The first electrode 101 (also referred to as an anode or bifunctional layer) is configured to receive a first stream 104 containing ammonia or decomposed ammonia products. In one embodiment, the decomposed ammonia products include hydrogen, nitrogen, and optionally ammonia. Stream 106 is an exhaust stream from the first electrode, or anode 101, containing, for example, ammonia, hydrogen, and nitrogen.

[0033] The second electrode or cathode 102 is configured to output a second stream 107 containing hydrogen. In embodiments, the hydrogen produced from the second electrode 102 is pure hydrogen, meaning that hydrogen is the predominant component in the gas phase produced from the second electrode. In some cases, the hydrogen content is 99.5% or greater. In some cases, the hydrogen content is 99.9% or greater. In some cases, the hydrogen produced from the second electrode is the same purity as hydrogen produced from the electrolysis of water. In various embodiments, the first and second streams are separated by a membrane.

[0034] In various embodiments, the device does not contain current collectors. In one embodiment, the device does not include interconnects. No electricity is required, and such a device is not an electrolyzer. This is a major advantage of the EC reactor of the present disclosure. The membrane 103 is configured to conduct electrons and is itself mixed conducting, i.e., both electronically and ionically conductive. In one embodiment, the membrane 103 conducts protons and electrons. In one embodiment, the electrodes 101, 102, and the membrane 103 are tubular (see Figures 2A and 2B). In one embodiment, the electrodes 101, 102, and the membrane 103 are planar. In these embodiments, the electrochemical reactions at the anode and cathode occur spontaneously without the need to apply a potential / electricity to the reactor.

[0035] In one embodiment, the reactor includes a porous electrode. In various embodiments, the electrode does not have a current collector attached. In various embodiments, the reactor does not contain a current collector. Clearly, such a reactor is fundamentally different from an electrolysis device or a fuel cell. In various embodiments, the anode, cathode, and membrane have the same elements.

[0036] In various embodiments, the anode, cathode, and membrane comprise a proton-conducting phase and an electron-conducting phase. In various embodiments, the proton-conducting phase is selected from the group consisting of barium zirconate cerate, yttrium-doped barium zirconate, BaHf x Ce 0.8-x Y 0.1 Yb0.1 O 3-δ (BHCYYb), BaZr x Ce 0.8-x Y 0.1 Yb 0.1 O 3-δ (BZCYYb), yttrium-doped barium zirconate cerate, or a combination thereof.

[0037] In various embodiments, the electronically conductive phase comprises doped lanthanum chromite, lanthanum-doped strontium titanate (LST), an electronically conductive metal, or a combination thereof. In various embodiments, the LST comprises LaSrCaTiO. In various embodiments, the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof. In various embodiments, the doped lanthanum chromite comprises strontium-doped lanthanum chromite, iron-doped lanthanum chromite, strontium- and iron-doped lanthanum chromite, lanthanum calcium chromite, or a combination thereof.

[0038] FIG. 2A illustrates (not to scale) a tubular electrochemical (EC) reactor 200 according to one embodiment of the present disclosure. The tubular reactor 200 includes an inner tubular structure 202, an outer tubular structure 204, and a membrane 206 disposed between the inner tubular structure 202 and the outer tubular structure 204, respectively. The tubular reactor 200 further includes a void space 208 for fluid passage. FIG. 2B illustrates (not to scale) a cross section of a tubular generator 200 according to one embodiment of the present disclosure. The tubular reactor 200 includes a first inner tubular structure 202, a second outer tubular structure 204, and a membrane 206 disposed between the inner tubular structure 202 and the outer tubular structure 204. The tubular reactor 200 further includes a void space 208 for fluid passage.

[0039] In one embodiment, the electrodes and membrane are tubular, with a first electrode or anode on the outermost side and a second electrode or cathode on the innermost side, the second electrode or cathode configured to output hydrogen. In one embodiment, the electrodes and membrane are tubular, with a first electrode or anode on the innermost side and a second electrode or cathode on the outermost side, the second electrode or cathode configured to output hydrogen. In one embodiment, the electrodes and membrane are tubular.

[0040] Hydrogen production using ammonia As discussed above, EC reactors are suitable for producing hydrogen from ammonia. Ammonia, or products of ammonia decomposition including hydrogen and nitrogen, are sent directly to the anode of the EC reactor as a feed stream. In various embodiments, in situ ammonia decomposition occurs at the anode.

[0041] Hydrogen dissociates into protons and electrons at the anode and is transported through the membrane to the cathode, where it recombines into molecular hydrogen. Because other gases (e.g., N2 or NH3) have no way to pass through the membrane to the cathode, hydrogen separation and purification is naturally achieved through an electrochemical route. In various embodiments, a pressure differential exists between the anode and cathode, further promoting hydrogen production at the cathode. In various embodiments, the cathode is configured to receive a vacuum. In various embodiments, the hydrogen partial pressure at the anode is higher than the hydrogen partial pressure at the cathode. In various embodiments, steam is introduced to the cathode.

[0042] The hydrogen produced is of sufficient purity for direct consumer use. In some cases, the hydrogen is used in FT reactors to produce synthetic fuels and / or synthetic lubricants. In some cases, the hydrogen is stored or used to generate electricity in electrochemical devices or as a fuel for automobiles. In some cases, the hydrogen is used in the Sabatier reaction. In some cases, the hydrogen is used to produce ammonia / fertilizer. In some cases, the hydrogen is used in hydrogenation processes.

[0043] In various embodiments, the reactor is configured to operate at a temperature of 500° C. or greater. In various embodiments, the reactor is configured to operate at a temperature of 600° C. or greater. In various embodiments, the reactor is configured to operate at a temperature of 700° C. or greater. In various embodiments, the reactor is configured to operate at a temperature of 800° C. or greater.

[0044] It should be understood that this disclosure describes exemplary embodiments for implementing different features, structures, or functions of the present invention. To simplify the disclosure, exemplary embodiments of components, arrangements, and configurations are described; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the present invention. Unless otherwise specified, the embodiments presented herein can be combined, and such combinations do not depart from the scope of the disclosure.

[0045] Additionally, specific terms are used throughout the description and claims to refer to particular components or steps. As one skilled in the art will appreciate, various entities may refer to the same component or process step by different names, and therefore, the naming conventions for elements described herein are not intended to limit the scope of the invention. Furthermore, the terminology and naming conventions used herein are not intended to distinguish between components, functions, and / or steps that differ in name but function.

[0046] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and description. It should be understood, however, that the drawings and detailed description are not intended to limit the disclosure to the particular forms disclosed, but on the contrary, are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

Claims

1. (a) providing an electrochemical reactor having an anode, a cathode, and a membrane between the anode and the cathode, wherein the membrane conducts both electrons and protons, and the anode and the cathode are porous; (b) introducing a first stream comprising ammonia or decomposed ammonia products into said anode; (c) extracting a second stream comprising hydrogen from the cathode, wherein the first stream and the second stream are separated by the membrane.

2. The method of claim 1 , wherein ammonia decomposition occurs in situ at the anode.

3. The method of claim 1 , comprising applying a vacuum to the cathode.

4. The method of claim 1 , wherein the membrane, the anode, and the cathode comprise the same elements.

5. The method of claim 1 , wherein the membrane, the anode, and the cathode comprise a proton-conducting phase and an electron-conducting phase.

6. The proton conducting phase is BaHf ｘ Ce ０．８－ｘ Y ０．１ Yb ０．１ O ３－δ (BHCYYb), BaZr ｘ Ce ０．８－ｘ Y ０．１ Yb ０．１ O ３－δ 6. The method of claim 5, comprising: (BZCYYb), yttrium-doped barium zirconate, yttrium-doped barium zirconate cerate, barium zirconate cerate, or a combination thereof.

7. 6. The method of claim 5, wherein the electronically conducting phase comprises doped lanthanum chromite, lanthanum doped strontium titanate (LST), an electronically conducting metal, or a combination thereof.

8. The method of claim 1 , wherein the hydrogen partial pressure at the anode is higher than the hydrogen partial pressure at the cathode.

9. a source of ammonia or a source of decomposed ammonia products; 1. A hydrogen generation system comprising: an electrochemical (EC) reactor having an anode, a cathode, and a membrane between the anode and the cathode, wherein the membrane conducts both electrons and protons, and the anode and the cathode are porous; the EC reactor is configured to receive a first stream from the ammonia source or the cracked ammonia product source on the anode side; The hydrogen generation system, wherein the EC reactor is configured to output a second stream to the cathode side, the second stream comprising hydrogen.

10. 10. The system of claim 9, wherein the reactor is interconnect-free and current collector-free.

11. The system of claim 9 , wherein the anode, the cathode, and the membrane comprise the same element.

12. The system of claim 9 , wherein the anode, the cathode, and the membrane comprise a proton-conducting phase and an electron-conducting phase.

13. The proton conducting phase is BaHf ｘ Ce ０．８－ｘ Y ０．１ Yb ０．１ O ３－δ (BHCYYb), BaZr ｘ Ce ０．８－ｘ Y ０．１ Yb ０．１ O ３－δ 13. The system of claim 12, comprising (BZCYYb), yttrium-doped barium zirconate, yttrium-doped barium zirconate cerate, barium zirconate cerate, or a combination thereof.

14. 13. The system of claim 12, wherein the electronically conducting phase comprises doped lanthanum chromite, lanthanum doped strontium titanate (LST), an electronically conducting metal, or a combination thereof.

15. The LST is LaSrCaTiO ３ The system of claim 14 , comprising:

16. 15. The system of claim 14, wherein the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof.

17. 15. The system of claim 14, wherein the doped lanthanum chromite comprises strontium-doped lanthanum chromite, iron-doped lanthanum chromite, strontium- and iron-doped lanthanum chromite, lanthanum calcium chromite, or a combination thereof.

18. The system of claim 9 , wherein the cathode is configured to receive a vacuum.

19. 10. The system of claim 9, wherein the first stream and the second stream are separated by the membrane.

20. 10. The system of claim 9, wherein the reactor is configured to operate at a temperature of 500°C or greater.

21. The system of claim 9 , wherein the hydrogen partial pressure at the anode is higher than the hydrogen partial pressure at the cathode.

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