Electrochemical hydrogen production using ammonia with oxidant injection

Abstract

The present invention provides 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, the membrane having both electronic and ionic conductivity; (b) introducing a first stream comprising ammonia to the anode; (c) introducing an oxidant to the anode; and (d) introducing a second stream comprising water to the cathode, the second stream providing a reducing environment at the cathode; wherein hydrogen is electrochemically produced from the water, the first stream and the second stream being separated by the membrane, and the oxidant and the second stream being separated by the membrane.

Description

[Technical Field]

[0001] The present invention relates generally to hydrogen production, and more particularly to electrochemical hydrogen production using ammonia with oxidant injection. [Background technology]

[0002] The petroleum and chemical industries require large quantities of hydrogen. For example, large amounts of hydrogen are used in the upgrading of fossil fuels and the production of methanol or hydrochloric acid. Petrochemical plants require hydrogen for hydrocracking, hydrodesulfurization, and hydrodealkylation. Hydrogen is also required for hydrogenation processes to increase the saturation of unsaturated fats and oils. Hydrogen is also a reducing agent for metal ores. Hydrogen can be produced from water electrolysis, steam reforming, laboratory-scale metal-acid processes, thermochemical methods, or anaerobic corrosion. Many countries are moving toward a hydrogen economy, requiring the transportation of large quantities 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 itself is not easily accessible and must be converted to hydrogen. Unfortunately, this conversion process produces hydrogen mixed with nitrogen, and separating these two gases simply, efficiently, or economically is difficult. To be effective in conventional systems and processes, the hydrogen must be separated from the nitrogen.

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

[0004] The present invention provides 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, the membrane having both electronic and ionic conductivity; (b) introducing a first stream comprising ammonia to the anode; (c) introducing an oxidant to the anode; and (d) introducing a second stream comprising water to the cathode, the second stream providing a reducing environment at the cathode; wherein hydrogen is electrochemically produced from the water, the first stream and the second stream being separated by the membrane, and the oxidant and the second stream being separated by the membrane.

[0005] In one embodiment, the oxidant comprises oxygen or air. In one embodiment, the molar ratio of ammonia to oxygen on the anode side is 2 or greater, 3 or greater, or 4 or greater. In one embodiment, ammonia pyrolysis occurs in situ at the anode. In one embodiment, the second stream comprises hydrogen. In one embodiment, a hydrocarbon is introduced to the anode. In one embodiment, the oxidant is added to the anode at multiple points along the flow path of the first stream.

[0006] In one embodiment, the anode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, and LSGM. In one embodiment, the cathode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and combinations thereof. In one embodiment, the membrane comprises CoCGO or LST (lanthanum-doped strontium titanate) stabilized zirconia. In one embodiment, LST comprises LCST (lanthanum- and calcium-doped strontium titanate). In one embodiment, the stabilized zirconia comprises YSZ, SSZ, or SCZ (scandiaceria-stabilized zirconia).

[0007] In one embodiment, the film includes an electronically conductive phase containing doped lanthanum chromite or an electronically conductive metal, or a combination thereof, and the film includes an ionically conductive phase containing a material selected from the group consisting of gadolinium-doped ceria (CGO), samarium-doped ceria (SDC), yttria-stabilized zirconia (YSZ), lanthanum strontium gallate magnesite (LSGM), scandia-stabilized zirconia (SSZ), Sc- and Ce-doped zirconia, and combinations thereof. In one embodiment, the doped lanthanum chromite includes strontium-doped lanthanum chromite, iron-doped lanthanum chromite, strontium- and iron-doped lanthanum chromite, lanthanum calcium chromite, or a combination thereof. In one embodiment, the conductive metal includes Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof.

[0008] The present invention also provides a hydrogen generation system that includes an ammonia source, an oxidant source, and an electrochemical (EC) reactor including an anode, a cathode, and a membrane between the anode and the cathode, the membrane having both electronic and ionic conductivity, wherein the EC reactor is configured to receive, at an anode side, a first flow from the ammonia source and an oxidant from the oxidant source, and at the cathode side, the EC reactor is configured to receive, at the cathode side, a second flow, the second flow including water, providing a reducing environment at the cathode.

[0009] In one embodiment, the anode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, and LSGM. In one embodiment, the cathode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and combinations thereof. In one embodiment, the membrane comprises CoCGO or LST (lanthanum-doped strontium titanate) stabilized zirconia. In one embodiment, LST comprises LCST (lanthanum- and calcium-doped strontium titanate). In one embodiment, the stabilized zirconia comprises YSZ, SSZ, or SCZ (scandiaceria-stabilized zirconia).

[0010] In one embodiment, the second stream comprises hydrogen. In one embodiment, the molar ratio of ammonia to oxidant on the anode side is 2 or greater, 3 or greater, or 4 or greater. In one embodiment, the anode is configured to receive a hydrocarbon. In one embodiment, the system includes a multi-position injection port in fluid communication with the reactor, the multi-position injection port configured to introduce the oxidant, the hydrocarbon, or both, to the anode. In one embodiment, the cathode is configured to electrochemically produce hydrogen from water. In one embodiment, the reactor does not include an interconnect or a current collector.

[0011] In one embodiment, the film comprises an electronically conductive phase containing doped lanthanum chromite or an electronically conductive metal, or a combination thereof, and the film comprises an ionically conductive phase containing a material selected from the group consisting of gadolinium-doped ceria (CGO), samarium-doped ceria (SDC), yttria-stabilized zirconia (YSZ), lanthanum strontium gallate magnesite (LSGM), scandia-stabilized zirconia (SSZ), Sc- and Ce-doped zirconia, and combinations 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, and the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof.

[0012] Further aspects and embodiments are described 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.

[0013] The following drawings are provided to illustrate certain embodiments described herein. The drawings are merely illustrative and do not limit the scope of the claimed invention, nor do they illustrate every possible feature or embodiment of the claimed invention. The drawings are not necessarily drawn to scale. 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]

[0014] [Figure 1] 1 illustrates an electrochemical (EC) reactor or electrochemical gas generator according to an embodiment of the present disclosure. [Figure 2A] 1 illustrates a tubular electrochemical reactor according to an embodiment of the present disclosure. [Figure 2B] 1 illustrates a cross section of a tubular electrochemical reactor according to an embodiment of the present disclosure. [Figure 3A] 1 illustrates a process and system for electrochemically producing hydrogen using ammonia according to an embodiment of the present disclosure. [Figure 3B] 1 illustrates an alternative process and system for electrochemically producing hydrogen using ammonia according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] overview Ammonia is an abundant and common chemical that is transported worldwide. Furthermore, ammonia (unlike hydrogen) does not need to be stored under high pressure or at cryogenic temperatures, and the energy density of ammonia is 10 times that of lithium-ion batteries. Therefore, utilizing ammonia to produce hydrogen would be highly advantageous if done efficiently and economically. This disclosure describes electrochemical systems and methods suitable for producing hydrogen using ammonia.

[0016] The following terms and phrases have the meanings indicated below, unless otherwise specified herein. Other terms and phrases may be used in this disclosure that are not expressly defined herein. Such other terms and phrases shall have the meaning they would have to one of ordinary skill in the art 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 include their plural counterparts, and vice versa, unless expressly stated to the contrary.

[0017] As used herein, the singular forms "a," "an," or "the" include plural referents unless the context clearly dictates otherwise. For example, the term "substituent" is intended to include not only a single substituent but also two or more substituents, etc. As used herein, the words "for example," "for instance," "such as," or "including" are intended to introduce examples that further clarify a more general subject matter. Unless expressly indicated otherwise, such examples are provided solely as an aid in understanding the embodiments described in this disclosure and are not meant to be limiting in any way. Furthermore, these terms do not imply any kind of preference for the disclosed embodiments.

[0018] As used herein, unless otherwise specified, the terms composition and material are used interchangeably. Each composition / material may contain multiple elements, phases, and components. Heating, as used herein, refers to the active application of energy to a composition or material.

[0019] 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.

[0020] In this disclosure, the absence of substantial amounts of H2 means that the volumetric hydrogen content is 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, 0.1% or less, or 0.05% or less.

[0021] As used herein, CGO refers to gadolinium-doped ceria, also known as gadolinia-doped ceria, gadolinium-doped cerium oxide, cerium(IV) oxide, gadolinium-doped, GDC, or GCO (formula Gd:CeO). Unless otherwise specified, CGO and GDC are used interchangeably. Syngas (i.e., synthesis gas) in this disclosure refers to a mixture consisting primarily of hydrogen, carbon monoxide, and carbon dioxide.

[0022] Mixed conducting membranes are capable of transporting both electrons and ions. Ionic conductivity includes ionic species such as oxygen ions (or oxide ions), protons, halide anions, and chalcogenide anions. In various embodiments, the mixed conducting membranes of the present disclosure include an electronically conducting phase and an ionically conducting phase.

[0023] In this disclosure, the tubular axial cross section is shown as circular, but this is for purposes of example only and not limitation, and the tubular axial cross section may be any suitable shape known to those skilled in the art, such as a square, a square with rounded corners, a rectangle, a rectangle with rounded corners, a triangle, a hexagon, a pentagon, an oval, an irregular shape, etc.

[0024] As used herein, ceria refers to cerium oxide, also known as cerium oxide, cerium dioxide, or cerium oxide, and 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 and includes all oxidation states of chromium oxide.

[0025] As used herein, an impermeable layer or material means impermeable to fluid flow, e.g., the permeability of an impermeable layer or material is less than 1 microdarcy, or less than 1 nanodarcy.

[0026] 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 extent that it becomes liquid. 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 together to form a single solid piece.

[0027] The term "in situ" in this disclosure refers to a treatment (e.g., heating or pyrolysis) process carried out at the same location or within the same apparatus. For example, ammonia pyrolysis occurring at an anode in an electrochemical reactor is considered in situ.

[0028] Electrochemistry is a branch of physical chemistry that deals with the relationship between electric potential as a measurable, quantitative phenomenon and the electric potential resulting from a specific chemical change, or vice versa. In these reactions, electrons are transferred between electrodes through an electronically conducting phase (typically, but not necessarily, an external electric circuit) separated by an ionically conducting and electronically insulating membrane (or ionic species in solution). When a chemical reaction is driven by a potential difference, as in electrolysis, or when an electric potential is generated by a chemical reaction, as in batteries or fuel cells, the reaction is called an electrochemical reaction. Unlike chemical reactions, in electrochemical reactions, electrons (and the resulting ions) are not transferred directly between molecules, but rather through the aforementioned electronic and ionic conduction circuits, respectively. This phenomenon distinguishes electrochemical reactions from chemical reactions.

[0029] In connection with electrochemical reactors and methods of using them, various reactor components, such as electrodes and membranes, and the materials of construction of the components are described. 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. Therefore, it does not necessarily include information that is known to one of ordinary skill in the art.

[0030] Interconnects in electrochemical devices (e.g., fuel cells) are often either metal or ceramic that 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, an interconnect, means a layer that is impermeable to fluid flow.

[0031] Electrochemical Reactor In contrast to conventional methods, electrochemical reactors containing ion-conducting membranes have been discovered that can electrochemically reform hydrocarbons or perform the water-gas shift reaction. In electrochemical reforming reactions, hydrocarbons are oxidized by the exchange of ions across a membrane. Electrochemical reactions involve the exchange of ions across a membrane and include the forward water-gas shift reaction, the reverse water-gas shift reaction, or both. These differ from traditional reforming and water-gas shift reactions via chemical routes because they involve the direct combination of reactants.

[0032] 1 illustrates an electrochemical reactor or electrochemical (EC) gas generator 100 according to an embodiment of the present disclosure. The electrochemical reactor (or EC gas generator) device 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 fuel 104. The stream 104 is oxygen-free. The second electrode 102 is configured to receive water (e.g., steam), as indicated at 105.

[0033] In one embodiment, the device 100 is configured to receive CO or H (104) and produce CO / CO or H O (106) at the first electrode (101), and the device 100 is also configured to receive water or steam (105) and produce hydrogen (107) at the second electrode (102). In some cases, the second electrode receives a mixture of steam and hydrogen. Water is considered the oxidant in this scenario because it provides the oxide ions (transported through the membrane) necessary to oxidize CO or H at the opposite electrode. Thus, the first electrode 101 is undergoing an oxidation reaction in a reducing environment. In various embodiments, 103 represents an oxide-ion conducting membrane. In one embodiment, the first electrode 101 and the second electrode 102 comprise Ni-YSZ or NiO-YSZ. In one embodiment, the oxide-ion conducting membrane 103 also conducts electrons. In these cases, gases containing H, CO, syngas, or combinations thereof are suitable as the feed stream 104. In various embodiments, electrodes 101 and 102 comprise Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and combinations thereof. Alternatively, the hydrocarbon-containing gas is reformed before contacting membrane 103 / electrode 101. The reformer is configured to perform steam reforming, dry reforming, or a combination thereof. The reformed gas is suitable as feed stream 104.

[0034] In one embodiment, device 100 is configured to co-produce hydrogen 107 from second electrode 102 and syngas 106 from first electrode 101. In one embodiment, 104 represents methane and water, or methane and carbon dioxide, entering device 100. In another embodiment, 104 represents methane. In another embodiment, 103 represents an oxide ion conducting membrane. Arrow 104 represents the inflow of hydrocarbons and water, or hydrocarbons and carbon dioxide. Arrow 105 represents the inflow of water or water and hydrogen. In some embodiments, electrode 101 comprises Cu-CGO or optionally further comprises CuO, CuO, or a combination thereof, and electrode 102 comprises Ni-YSZ or NiO-YSZ. In some cases, electrode 101 includes doped or undoped ceria and a material selected from the group consisting of Cu, CuO, Cu2O, Ag, Ag2O, Au, Au2O, Au2O3, Pt, Pd, Ru, Rh, Ir, LaCaCr, LaSrCrFe, YSZ, CGO, SDC, SSZ, LSGM, stainless steel, and combinations thereof, and electrode 102 includes Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and combinations thereof. In some cases, electrode 101 includes lanthanum chromite and a material selected from the group consisting of doped ceria, yttria-stabilized zirconia (YSZ), lanthanum strontium gallate magnesite (LSGM), scandia-stabilized zirconia (SSZ), zirconia doped with Sc and Ce, and combinations thereof, and electrode 102 includes Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and combinations thereof. In various embodiments, the lanthanum chromite includes undoped lanthanum chromite, strontium-doped lanthanum chromite, iron-doped lanthanum chromite, strontium- and iron-doped lanthanum chromite, lanthanum calcium chromite, or combinations thereof.

[0035] Arrow 104 represents the inflow of hydrocarbons with little or no water and no carbon dioxide or oxygen, while arrow 105 represents the inflow of water or water and hydrogen. Water is considered the oxidant in this scenario because it provides the oxide ions (transported through the membrane) necessary to oxidize the hydrocarbon / fuel at the opposite electrode. In these cases, a hydrocarbon-containing gas is suitable as the feed stream 104, and no gas reforming is required. In these cases, the reactor enables electrochemical reforming, and the oxygen needed to reform methane is obtained from the reduction of water and fed through the membrane. The half-cell reactions are electrochemical and are as follows: [ka] [ka]

[0036] In this disclosure, oxygen-free means that there is no oxygen present at the first electrode 101, or at least not enough oxygen to interfere with the reaction. Also, in this disclosure, water only means that the intended source is water, and does not exclude trace elements or inherent components in water. For example, water containing salts or ions is considered within the scope of water-only. While water-only does not necessarily have to be 100% pure, this embodiment is included. In one embodiment, 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 purity of the hydrogen produced from the second electrode is the same as the purity of hydrogen produced from the electrolysis of water.

[0037] In one embodiment, the first electrode 101 is configured to receive methane, or methane and water, or methane and carbon dioxide. In one embodiment, the fuel comprises a hydrocarbon having a carbon number in the range of 1 to 12, 1 to 10, or 1 to 8. Most preferably, the fuel is methane or natural gas that is primarily methane. In one embodiment, the device does not generate electricity and is not a fuel cell.

[0038] In various embodiments, the device does not contain a current collector. In one embodiment, the device does not include interconnects. No electricity is required, and such a device is not an electrolysis device. This is a major advantage of the EC reactor of the present disclosure. The membrane 103 is configured to conduct electrons and is mixed conductive, i.e., includes both electronic and ionic conductivity. In one embodiment, the membrane 103 conducts oxide ions and electrons. In one embodiment, the electrodes 101, 102 and the membrane 103 are tubular (see, e.g., 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 an electrical potential / electricity to the reactor.

[0039] In one embodiment, an electrochemical reactor (or EC gas generator) is a device including a first electrode, a second electrode, and a membrane between the electrodes, wherein the first electrode and the second electrode include a metal phase that is free of platinum group metals during use of the device, and the membrane is oxide-ion conductive. In one embodiment, the first electrode is configured to receive a fuel. In one embodiment, the fuel includes a hydrocarbon, hydrogen, carbon monoxide, or a combination thereof. In one embodiment, the second electrode is configured to receive water and hydrogen and is configured to reduce water to hydrogen. In various embodiments, such reduction occurs electrochemically.

[0040] In one embodiment, the film comprises an electronically conductive phase containing doped lanthanum chromite or an electronically conductive metal, or a combination thereof, and the film comprises an ionically conductive phase containing a material selected from the group consisting of gadolinium-doped ceria (CGO), samarium-doped ceria (SDC), yttria-stabilized zirconia (YSZ), lanthanum strontium gallate magnesite (LSGM), scandia-stabilized zirconia (SSZ), Sc- and Ce-doped zirconia, and combinations 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, and the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof. In one embodiment, the film comprises gadolinium-doped ceria (CGO) or samarium-doped ceria (SDC). In one embodiment, the film consists of gadolinium-doped ceria (CGO) or samarium-doped ceria (SDC).

[0041] In some cases, the membrane comprises a single phase of mixed ionic and electronic conductivity. In one embodiment, the membrane comprises cobalt-CGO (CoCGO), i.e., CGO doped with cobalt. In one embodiment, the membrane consists essentially of CoCGO. In one embodiment, the membrane consists of CoCGO.

[0042] In one embodiment, the membrane comprises LST (lanthanum-doped strontium titanate)-YSZ, LST-SSZ, or LST-SCZ (scandiaceria-stabilized zirconia). In various embodiments, the LST comprises LCST (lanthanum- and calcium-doped strontium titanate). In one embodiment, the membrane consists essentially of LST-YSZ, LST-SSZ, or LST-SCZ. In one embodiment, the membrane consists of LST-YSZ, LST-SSZ, or LST-SCZ. In this disclosure, LST-YSZ refers to a composite of LST and YSZ. In various embodiments, the LST and YSZ phases interpenetrate. In this disclosure, LST-SSZ refers to a composite of LST and SSZ. In various embodiments, the LST and SSZ phases interpenetrate. In this disclosure, LST-SCZ refers to a composite of LST and SCZ. In various embodiments, the LST and SCZ phases interpenetrate. YSZ, SSZ, and SCZ are types of stabilized zirconia. In one embodiment, the membrane comprises CoCGO or LST (lanthanum-doped strontium titanate) stabilized zirconia. In one embodiment, the stabilized zirconia comprises YSZ, SSZ, or SCZ (scandiaceria stabilized zirconia).

[0043] FIG. 2A illustrates (not to scale) a tubular electrochemical (EC) reactor or EC gas generator 200 according to an embodiment of the present disclosure. The tubular generator 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. The tubular generator 200 further includes a void space 208 for a fluid to pass through. FIG. 2B illustrates (not to scale) a cross section of the tubular generator 200 according to an embodiment of the present disclosure. The tubular generator 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 generator 200 further includes a void space 208 for a fluid to pass through.

[0044] In one embodiment, the electrodes and membrane are tubular, with a first electrode being outermost and a second electrode being innermost, the second electrode being configured to receive water and hydrogen. In one embodiment, the electrodes and membrane are tubular, with a first electrode being innermost and a second electrode being outermost, the second electrode being configured to receive water and hydrogen. In one embodiment, the electrodes and membrane are tubular.

[0045] Hydrogen generation using ammonia The EC reactor described above is suitable for producing hydrogen from ammonia. The products from ammonia pyrolysis, including hydrogen and nitrogen, are sent directly to the anode of the EC reactor as a feed stream. In one embodiment, the reactor includes porous electrodes including a metallic phase and a ceramic phase, where the metallic phase is electronically conductive and the ceramic phase is ionically conductive. In various embodiments, the electrodes are not equipped with current collectors. In various embodiments, the reactor does not include any current collectors. Clearly, such a reactor is fundamentally different from any electrolyzer or fuel cell.

[0046] In one embodiment, one of the electrodes in the reactor is an anode configured to be exposed to a reducing environment while electrochemically carrying out an oxidation reaction, hi one embodiment, the electrode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and combinations thereof.

[0047] The electrochemical reactions occurring within the reactor include electrochemical half-cell reactions, which are as follows: [ka] [ka]

[0048] In various embodiments, the half-cell reactions occur at a three-phase boundary, which is the intersection of the electronically and ionically conducting phases and the pores. Additionally, the reactor is also capable of performing the chemical water-gas shift reaction. In various embodiments, the ammonia pyrolysis products include hydrogen and nitrogen, and hydrogen is a suitable fuel for the anode of the EC reactor. An advantage of this method and system is that the presence of nitrogen does not affect the performance of the EC reactor and the production of hydrogen at the cathode.

[0049] In various embodiments, the ion-conducting membrane conducts protons or oxide ions. In various embodiments, the ion-conducting membrane comprises a solid oxide. In various embodiments, the ion-conducting membrane is impermeable to fluid flow. In various embodiments, the ion-conducting membrane also conducts electrons, and the reactor does not include interconnects.

[0050] In one embodiment, the film comprises an electronically conductive phase containing doped lanthanum chromite or an electronically conductive metal, or a combination thereof, and the film comprises an ionically conductive phase containing a material selected from the group consisting of gadolinium-doped ceria (CGO), samarium-doped ceria (SDC), yttria-stabilized zirconia (YSZ), lanthanum strontium gallate magnesite (LSGM), scandia-stabilized zirconia (SSZ), Sc- and Ce-doped zirconia, and combinations 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, and the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof. In one embodiment, the film comprises gadolinium-doped ceria (CGO) or samarium-doped ceria (SDC). In one embodiment, the film consists of gadolinium-doped ceria (CGO) or samarium-doped ceria (SDC).

[0051] In some cases, the membrane comprises a single phase of mixed ionic and electronic conductivity. In one embodiment, the membrane comprises cobalt-CGO (CoCGO), i.e., CGO doped with cobalt. In one embodiment, the membrane consists essentially of CoCGO. In one embodiment, the membrane consists of CoCGO.

[0052] In one embodiment, the membrane comprises LST (lanthanum-doped strontium titanate)-YSZ, LST-SSZ, or LST-SCZ (scandiaceria-stabilized zirconia). In various embodiments, the LST comprises LCST (lanthanum- and calcium-doped strontium titanate). In one embodiment, the membrane consists essentially of LST-YSZ, LST-SSZ, or LST-SCZ. In one embodiment, the membrane consists of LST-YSZ, LST-SSZ, or LST-SCZ. In this disclosure, LST-YSZ refers to a composite of LST and YSZ. In various embodiments, the LST and YSZ phases interpenetrate. In this disclosure, LST-SSZ refers to a composite of LST and SSZ. In various embodiments, the LST and SSZ phases interpenetrate. In this disclosure, LST-SCZ refers to a composite of LST and SCZ. In various embodiments, the LST and SCZ phases interpenetrate. YSZ, SSZ, and SCZ are types of stabilized zirconia. In one embodiment, the membrane comprises CoCGO or LST (lanthanum-doped strontium titanate) stabilized zirconia. In one embodiment, the stabilized zirconia comprises YSZ, SSZ, or SCZ (scandiaceria stabilized zirconia).

[0053] As shown in FIG. 3A, an ammonia-based hydrogen production system 3000 is shown. The system 3000 includes an EC reactor 331, an ammonia source 321, and an oxidant source 311. The EC reactor includes an anode 301, a cathode 302, and a membrane 303 between the anode and cathode. In various embodiments, the membrane 303 is mixed conducting. An ammonia stream 322 from the ammonia source 321 is sent to the anode 301 of the EC reactor 331. The oxidant source 311 supplies oxygen or air (stream 312) to the anode 301 of the reactor 331. The ammonia to oxygen molar ratio on the anode side is 2, 3, or 4 or greater. The anode exhaust is extracted as stream 306. The cathode 302 of the EC reactor 331 is configured to receive water / steam 304 and produce hydrogen (stream 305). The hydrogen is produced electrochemically by reducing water at the cathode. Optionally, stream 304 may further contain hydrogen. The atmosphere on the cathode side is a reducing environment.

[0054] Ammonia is partially oxidized on the anode side, providing the heat required for in-situ ammonia pyrolysis. The gas produced is suitable for use at the anode without the need to separate inert gases (nitrogen, water / steam, etc.) from the hydrogen. These inert gases do not significantly affect the kinetics or thermodynamics of the electrochemical reaction that produces hydrogen on the cathode side. This is a unique advantage of using the EC reactor of the present disclosure. In various cases, hydrocarbons (e.g., methane) are added to the anode 301 (not shown in FIG. 3A) and oxidized to generate additional heat for ammonia pyrolysis and / or the reactor. Carbon dioxide, as an oxidation product, also does not significantly affect the kinetics or thermodynamics of the electrochemical reaction.

[0055] As shown in Figure 3B, an alternative hydrogen production system 3001 utilizing ammonia is shown. A multi-position injection port 341 is added between the oxidant source 311 and the EC reactor 331. The oxidant stream 312 through the injection port 341 is introduced into the anode (301) side of the reactor 331 as streams 342-346. The injection port allows the oxidant to be added along the flow path of the anode feed stream, allowing for more precise control of the oxidation reaction and providing the heat required for the reactor and / or ammonia pyrolysis. Hydrocarbons (e.g., methane) can also be added to the anode 301 through the injection port (not shown in Figure 3B) and oxidized to generate additional heat for ammonia pyrolysis and / or the reactor.

[0056] It should be understood that this disclosure describes exemplary embodiments for implementing various features, structures, or functions of the present invention. While exemplary embodiments of components, arrangements, and configurations are described to simplify the disclosure, these exemplary embodiments are provided as examples only and are not intended to limit the scope of the present invention. The embodiments presented herein can be combined unless otherwise specified. Such combinations do not depart from the scope of the present disclosure.

[0057] Furthermore, certain terms are used throughout the specification 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, features and / or steps that differ in name but not function.

[0058] 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. 1. 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, the membrane having both electronic and ionic conductivity; (b) introducing a first stream comprising ammonia into the anode; (c) introducing an oxidizing agent to the anode; (d) introducing a second stream to the cathode, the second stream comprising water and providing a reducing environment at the cathode; Hydrogen is produced electrochemically from water, the first stream and the second stream are separated by the membrane; The method for producing hydrogen, wherein the oxidant and the second stream are separated by the membrane.

2. The method of claim 1 , wherein the oxidizing agent comprises oxygen or air.

3. 10. The method of claim 1, wherein the molar ratio of ammonia to oxygen in the anode side is 2 or more, 3 or more, or 4 or more.

4. 10. The method of claim 1, wherein ammonia pyrolysis occurs in situ at the anode.

5. The method of claim 1 , wherein the second stream comprises hydrogen.

6. The method of claim 1 , comprising introducing a hydrocarbon to the anode.

7. The method of claim 1 , wherein the oxidant is added to the anode at multiple points along the flow path of the first stream.

8. 10. The method of claim 1, wherein the anode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and the cathode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and combinations thereof.

9. 10. The method of claim 1, wherein the film comprises CoCGO or LST (lanthanum doped strontium titanate) stabilized zirconia, optionally wherein LST comprises LCST (lanthanum and calcium doped strontium titanate), and optionally wherein the stabilized zirconia comprises YSZ, SSZ, or SCZ (scandiaceria stabilized zirconia).

10. 2. The method of claim 1, wherein the film comprises an electronically conducting phase containing doped lanthanum chromite or an electronically conducting metal or a combination thereof, and the film comprises an ionically conducting phase containing a material selected from the group consisting of gadolinium-doped ceria (CGO), samarium-doped ceria (SDC), yttria-stabilized zirconia (YSZ), lanthanum strontium gallate magnesite (LSGM), scandia-stabilized zirconia (SSZ), Sc- and Ce-doped zirconia, and combinations thereof; optionally, 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; and optionally, the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof.

11. 1. A hydrogen production system comprising: a source of ammonia; a source of oxidant; an electrochemical (EC) reactor comprising an anode, a cathode, and a membrane between the anode and the cathode, the membrane having both electronic and ionic conductivity; the EC reactor is configured to receive, at the anode side, a first flow from the ammonia source and an oxidant from the oxidant source; The hydrogen generation system, wherein the EC reactor is configured to receive a second stream at the cathode side, the second stream comprising water and providing a reducing environment at the cathode.

12. 12. The system of claim 11, wherein the anode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and the cathode comprises Ni or NiO and a material selected from the group consisting of YSZ, CGO, SDC, SSZ, LSGM, and combinations thereof.

13. 12. The system of claim 11, wherein the film comprises CoCGO or LST (lanthanum doped strontium titanate) stabilized zirconia, optionally wherein LST comprises LCST (lanthanum and calcium doped strontium titanate), and optionally wherein the stabilized zirconia comprises YSZ, SSZ, or SCZ (scandiaceria stabilized zirconia).

14. The system of claim 11 , wherein the second stream comprises hydrogen.

15. 12. The system of claim 11, wherein the molar ratio of ammonia to oxidant on the anode side is 2 or greater, 3 or greater, or 4 or greater.

16. The system of claim 11 , wherein the anode is configured to receive a hydrocarbon.

17. 12. The system of claim 11, comprising a multi-position injection port in fluid communication with the reactor, the multi-position injection port configured to introduce an oxidant, a hydrocarbon, or both, to the anode.

18. The system of claim 11 , wherein the cathode is configured to electrochemically produce hydrogen from water.

19. 12. The system of claim 11 , wherein the film comprises an electronically conducting phase containing doped lanthanum chromite or an electronically conducting metal or a combination thereof, and the film comprises an ionically conducting phase containing a material selected from the group consisting of gadolinium-doped ceria (CGO), samarium-doped ceria (SDC), yttria-stabilized zirconia (YSZ), lanthanum strontium gallate magnesite (LSGM), scandia-stabilized zirconia (SSZ), Sc- and Ce-doped zirconia, and combinations thereof; and optionally, 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; and the conductive metal comprises Ni, Cu, Ag, Au, Pt, Rh, Co, Ru, or a combination thereof.

20. The system described in claim 11, wherein the EC reactor does not include any interconnects or current collectors.

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